MA H
GTP-BINDING
PROTEINS IN PLANTS - NEW MEMBERS OF AN OLD FAMILY
PLANT MOL BIOL 26 (5): 1611-1636 DEC 1994
Abstract:
Regulatory guanine nucleotide-binding proteins (G proteins) have been studied
extensively in animal and microbial organisms, and they are divided into the heterotrimeric and the small (monomeric)
classes. Heterotrimeric G proteins are known to
mediate signal responses in a variety of pathways in animals and simple
eukaryotes, whiole small G proteins perform diverse
functions including signal transduction, secretion, and regulation of
cytoskeleton. In recent years, biochemical analyses have produced a large
amount of information on the presence and possible functions of G proteins in
plants. Further, molecular cloning has clearly demonstrated that plants have
both heterotrimeric and small G proteins. Although
the functions of the plant heterotrimeric G proteins
are yet to be determined, expression analysis of an Arabidopsis Ga protein suggests that it may be involved in the
regulation of cell division and differentiation. In contrast to the very few
genes cloned thus far that encode heterotrimeric G
proteins in plants, a large number of small G proteins have been identified by
molecular cloning from various plants. In addition, several plant small G
proteins have been shown to be functional homologues of their counterparts in
animals and yeasts. Future studies using a number of approaches are likely to
yield insights into the role plant G proteins play.
VALIN P, GOULARD B, SANIELEVICI M
TOPOLOGY
DEPENDENCE IN LATTICE SIMULATIONS OF NONLINEAR PDES ON A MIMD COMPUTER
INT J MOD PHYS C 5 (6): 957-971 DEC 1994
Abstract:
We tested the parallelization of explicit schemes for the solution of
non-linear classical field theories of complex scalar fields which are capable
of simulating; hadronic collisions. Our attention
focused on collisions in a fractional model with a particularly rich inelastic
spectrum of final states. Relativistic collisions of all types were performed
by computer on large lattices (64 to 256 sites per dimension). The stability and
accuracy of the objects were tested by the use of two other methods of
solutions: Pseudo-spectral and semi-implicit. Parallelization of the Fortran code on a 64-transputer MIMD Volvox
machine revealed, for certain topologies, communication deadlock and less-than-optimum
routing strategies when the number of transputers
used was less than the maximum. The observed speedup, for N transputers
in an appropriate topology, is shown to scale approximately as N, but the
overall gain in execution speed, for physically interesting problems, is a
modest 2-3 when compared to state-of-the-art workstations.
SCHULZE E, NAGEL S, GAVENIS K, et al.
STRUCTURALLY
DIVERGENT HISTONE H1 VARIANTS IN CHROMOSOMES CONTAINING HIGHLY CONDENSED
INTERPHASE CHROMATIN
J CELL BIOL 127 (6): 1789-1798 Part 2 DEC 1994
Abstract:
Condensed and late-replicating interphase chromatin
in the Dipertan insect Chironomus
contains a divergent type of histone H1 with an
inserted KAPKAP repeat that is conserved in single H1 variants of Caenorhabditis elegans and Volvox carteri. H1
peptides comprising the insertion interact specifically with DNA. The Chironomid Glyptotendipes
exhibits a corresponding correlation between the presence of condensed
chromosome sections and the appearance of a divergent H1 subtype. The centromere regions and other sections of Glyptotendipes barbipes
chromosomes are inaccessible to immunodecoration by
anti-H2B and anti-H1 antibodies one of which is known to recognize nine
different epitopes in all domains of the H1 molecule.
Microelectrophoresis of the histones
from manually isolated unfixed centromeres revealed
the presence of H1 and core histones. H1 genes of G. barpipes were sequenced and found to belong to two groups.
H1 II and H1 III are rather similar but differ remarkably from H1 I. About 30%
of the deduced amino acid residues were found to be unique to H1 I. Most
conspicuous is the insertion, SPAKSPGR, in H1 I that is lacking in H1 II and H1
III and at its position gives rise to the sequence repeat SPAKSPAKSPGR. The
homologous H1 I gene in Glyptotendipes salinus encodes the very similar repeat TPAKSPAKSPGR. Both
sequences are structurally related to the KAPKAP repeat in H1 I-1 specific for
condensed chromosome sites in Chironomus and to the
SPKKSPKK repeat in sea urchin sperm H1, lie at almost the same distance from
the central globular domain, and could interact with linker DNA in packaging
condensed chromatin.
WOESSNER JP, MOLENDIJK AJ, VANEGMOND P, et al.
DOMAIN
CONSERVATION IN SEVERAL VOLVOCALEAN CELL-WALL PROTEINS
PLANT MOL BIOL 26 (3): 947-960 NOV 1994
Abstract:
Based on our previous work demonstrating that (SerPro)(x)
epitopes are common to extensin-like
cell wall proteins in Chlamydomonas reinhardtii, we looked for similar proteins in the
distantly related species C. euganzetos. Using a
polyclonal antiserum against a (SerPro)(10) oligopeptide, we found
distinct sets of stage-specific polypeptides immunoprecipitated
from in vitro translations of C. eugametos RNA.
Screening of a C. eugametos cDNA
expression library with the antiserum led to the isolation of a cDNA (WP6) encoding a (SerPro)(x)-rich multidomain wall
protein. Analysis of a similarly selected cDNA
(VSP-3) from a C. reinhardtii cDNA
expression library revealed that it also coded for a (SerPro)(x)-rich multidomain wall
protein. The C-terminal rod domains of VSP-3 and WP6 are highly homologous,
while the N-terminal domains are dissimilar; however, the N-terminal domain of
VSP-3 is homologous to the globular domain of a cell wall protein from Volvox carteri. Exon shuffling might be responsible for this example of domain
conservation over 350 million years of volvocalean
cell wall protein evolution.
DIETMAIER W, FABRY S
ANALYSIS OF
THE INTRONS IN GENES ENCODING SMALL G-PROTEINS
CURR GENET 26 (5-6): 497-505 NOV-DEC 19
Abstract:
Because all small G proteins (SGPs) possess a very
similar array of structural and functional domains, they are obvious candidates
for examining the relationships postulated to exist between the exon-intron structure of genes and the domain structure of
the encoded proteins. To address this issue, and to possibly gain insight into
the evolution of their introns, we have analyzed
positions, sizes, and sequences of 125 introns from
28 SGP genes. These introns were found to be
distributed in 60 different locations throughout the aligned sequences, with a
preference for the 5'-half of the genes. More than 50% of the positions were
found to be shared by two or more genes, and genes encoding SGPs
of very similar amino acid sequence (i.e., isotypes)
in quite closely related species tend to have most, or all, of their introns in identical locations, indicating a common
evolutionary origin (homologous introns). However,
with few exceptions, no statistically significant sequence similarity or common
folding motif was found between homologous intron
pairs. Only three intron positions are shared between
members of distantly related SGP subfamilies. These three potentially ancient intron locations fall between
regions encoding alpha-helices or beta-sheets, but two of them interrupt
regions encoding known functional (guanosine-nucleotide-binding)
modules. Intron positions that are occupied only in
single genes, or in genes encoding very similar SGPs,
do not show any preferential distribution with respect to regions encoding
structural or functional motifs. This discordance between exon
modules and structural and/or functional protein domains suggests that most, if
not all, introns in modern SGP genes arose by independent
insertion events after diversification of the various SGP subfamilies, and
therefore probably did not participate in the early evolution of these genes.
HALLMANN A, SUMPER M
REPORTER
GENES AND HIGHLY REGULATED PROMOTERS AS TOOLS FOR TRANSFORMATION EXPERIMENTS IN
VOLVOX-CARTERI
P NATL ACAD SCI USA 91 (24): 11562-11566 NOV 22 1994
Abstract:
The multicellular alga Volvox
is an attractive model for the study of developmental processes. With the
recent report of successful transformation, regulated promoters as well as
reporter genes working in this organism are now required. The Volvox genes encoding arylsulfatase
and the extracellular glycoprotein ISG are strictly
regulated. The former is transcribed only under conditions of sulfur
starvation, whereas the latter operates under extreme developmental control-i.e., it is transcribed for only a few minutes in Volvox embryos at the stage of embryonic inversion.
The gene encoding the sexual pheromone of Volvox
carteri was placed under the control of the arylsulfatase promoter. In response to sulfur deprivation,
V. carteri transformed by this construct synthesized
and secreted biologically active pheromone. In addition, the gene encoding Volvox arylsulfatase was
placed under the control of the ISG promoter. Transformed algae synthesized arylsulfatase mRNA only during embryonic inversion. These
experiments demonstrate the usefulness of both the arylsulfatase
and the sexual.
WOESSNER JP, GOODENOUGH UW
VOLVOCINE
CELL-WALLS AND THEIR CONSTITUENT GLYCOPROTEINS - AN EVOLUTIONARY PERSPECTIVE
PROTOPLASMA 181 (1-4): 245-258 1994
Abstract:
Similarities in the composition of the extracellular
matrix suggest that only some species of the unicellular Chlamydomonas
are closely related to the colonial and multicellular
flagellated members of the family Volvocaceae. The
cell walls from all of the algae in this volvocine
group contain a crystalline layer. This lattice structure can be used as a phylogenetic marker to divide Chlamydomonas
species into distinct classes, only one of which includes the volvocacean algae. Similarly, not all species of Chlamydomonas are sensitive to each other's cell wall lytic enzymes, implying divergence of the enzyme's inner
wall substrate. Interspecific reconstitution of the
crystalline layer is possible between C. reinhardtii
and the multicellular Volvox
carteri, but not between C. reinhardtii
and C. eugametos. The hydroxyproline-rich
glycoproteins (HRGPs) which
make up the crystalline layer in genera which have a similar crystal structure
exhibit many homologies. Interestingly, the evolutionarily distant cell walls
of C. reinhardtii and C. eugametos
also contain some HRGPs displaying a few
morphological and amino acid sequence homologies. The morphological
similarities between the flagellar agglutinins (HRGPs responsible for sexual recognition and adhesion
during the mating reaction) and the cell wall HRGPs
leads to the proposal of a superfamily from which
novel HRGPs (designed for self-assembly/recognition)
can constantly evolve. Just as Variations in the wall HRGPs
can lead to unique wall structures, new agglutinins facilitate sexual isolation
of new species. Thus, the HRGPs could emerge as
Valuable phylogenetic markers.
HUBER O, SUMPER M
ALGAL-CAMS -
ISOFORMS OF A CELL-ADHESION MOLECULE IN EMBRYOS OF THE ALGA VOLVOX WITH HOMOLOGY TO DROSOPHILA
FASCICLIN-I
EMBO J 13 (18): 4212-4222
Abstract:
Proof that plants possess homologs of animal adhesion
proteins is lacking. In this paper we describe the generation of monoclonal
antibodies that interfere with cell-cell contacts in the 4-cell embryo of the multicellular alga Volvox carteri, resulting in a hole between the cells. The number
of following cell divisions is reduced and the cell division pattern is altered
drastically. Antibodies given at a later stage of embryogenesis specifically
inhibit inversion of the embryo, a morphogenetic movement that turns the embryo
inside out. Immunofluorescence microscopy localizes
the antigen (Algal-CAM) at cell contact sites of the
NASS N, MOKA R, JAENICKE L
ADENYLYL-CYCLASE
FROM THE GREEN-ALGA VOLVOX-CARTERI
F NAGARIENSIS - PARTIAL-PURIFICATION AND CHARACTERIZATION
AUST J PLANT PHYSIOL 21 (5): 613-622 1994
Abstract:
In order to understand changes in cyclic adenylate
levels of Volvox carteri
during the process of sexual induction, we investigated the biochemical
properties of its membrane-bound adenylyl cyclase. Membrane preparations possess low levels of Mg2+-dependent
or Mn2+-dependent adenylyl cyclase
activity. This activity was solubilised and then
purified 7800-fold. The enzyme detergent complex has an apparent molecular mass
of 100 kDa. Purified preparations contain a major
ATP-binding protein of 33 kDa as shown by affinity labelling. The Mg2+-dependent basal enzyme activity is
regulated by Ca2+, and is highest in the presence of 10(-7) M Ca2+, but is
inhibited by Ca2+ above 10(-5) M. La3+ at 10(-4) M also blocks activity.
Neither calmodulin nor its antagonists affect the
enzyme activity, nor do the purified preparations interact with immobilised calmodulin. Further
mediators of G-protein action (NaF, or GTP and its
derivatives) and forskolins have no influence on the
basal activity of this plant enzyme. The function of adenylyl
cyclase in sexual induction of Volvox
is discussed.
HOOPS HJ, LONG JJ, HILE ES
FLAGELLAR
APPARATUS STRUCTURE IS SIMILAR BUT NOT IDENTICAL IN VOLVULINA-STEINII,
EUDORINA-ELEGANS, AND PLEODORINA-ILLINOISENSIS (CHLOROPHYTA) - IMPLICATIONS FOR
THE VOLVOCINE EVOLUTIONARY LINEAGE
J PHYCOL 30 (4): 679-689 AUG 1994
Abstract:
The colonial and multicellular members of the Volvocales can be arranged in order of increasing size and
complexity as the ''volvocine series.'' This series
is often assumed to reflect an evolutionary progression. The flagellar apparatuses of previously examined algae are not
consistent with a simple lineage. The flagellar
apparatuses of Astrephomene gubernaculifera
Pocock, Gonium pectorale
Muller, Platydorina caudata
Kofoid, Volvox rousseletii G. S. West, and V. carteri
f. weismannia (Powers) Iyengar
differ from one another, and there is no apparent progression in flagellar apparatus features from the simple to complex
colonial forms. We examined the flagellar apparatuses
of Volvulina steinii Playfair, Eudorina elegans Ehr., and Pleodorina illinoisensis Kofoid and found
then to be similar to one another. The basal bodies ave
connected by a distal fiber that is offset to the anti side of the cell. Two microtubular rootlets originate on the inside of the basal
bodies and extend toward the syn side. The other two
rootlets are oriented perpendicular to the first two and are anti-parallel to
each other. A coarsely striated component underlies the four-membered rootlets and extends to the basal bodies. A
proximal fiber complex connects the two basal bodies. This complex consists of
a branched striated component on the cis side of each
basal body. One part extends toward the anti side of the cell, while the other
extends into a fibrous component that runs between basal bodies. An additional
structure extends in the anti direction from the trans
side of each basal body. A fibrous component extends past one basal body in all
four species. This component goes past the trans basal
body in Volvulina steinii
and the cis basal body in E. elegans
and P. illinoisensis. The flagellar
apparatuses of these organisms are similar to those of G. pectorale
and Volvox carteri
but different from the other colonial volvocalean
algae examined. The algae examined in this study plus G. pectorale
and V. carteri probably share a common evolutionary
history that postdates the transition from the unicellular to colonial habit.
Such a shared evolutionary history is a requirement of the volvocine
hypothesis. However, we have not observed progressive changes in the flagellar apparatus correlated with increasing cell number,
differentiation, and sexual specialization. Thus, it is possible, but not
certain, that G. pectorale, Volvulina
steinii, E. elegans, P. illinoisensis, and Volvox carteri may form part of a volvocine
lineage.
KIRK DL
GERM-CELL
SPECIFICATION IN VOLVOX-CARTERI
CIBA F SYMP 182: 2-15 1994
Abstract:
Volvox carteri
illustrates with diagrammatic clarity Weismann's
concept of an immortal germline that produces a
mortal soma that will carry it for a time, but then perish. Each V. carteri adult consists of about 16 asexual reproductive
cells (gonidia) in the interior of a sphere that
consists at its surface of about 2000 biflagellate somatic cells. When mature,
each gonidium divides to form a juvenile with this
same cellular composition. Half-way through their maturation, juveniles hatch
out of the parenteral spheroid, whereupon parental
somatic cells undergo programmed death while juvenile gonidia
prepare for a new round of reproduction. The first visible step in V. carteri germ-soma differentiation is asymmetric cleavage,
which sets apart large gonidial initials from small
somatic initials. Experimental analysis indicates that it is a difference in
size, not any difference in cytoplasmic quality, that determines whether a cell will become germinal
or somatic. Mutational and molecular studies lead to the following model for
the genetic control of the germ-soma dichotomy: first, the gls
locus acts to cause asymmetric division; then large cells activate a set of lag
loci that suppress expression of somatic genes, while small cells activate the regA locus that suppresses gonidial
genes.
SCHIEDLMEIER B, SCHMITT R, MULLER W, et al.
NUCLEAR
TRANSFORMATION OF VOLVOX-CARTERI
P NATL ACAD SCI
Abstract:
Stable nuclear transformation of Volvox carteri was achieved using the cloned V. carteri nitA(+) gene (which
encodes nitrate reductase) to complement a nitA(-) mutation. Following bombardment of mutant cells
with plasmid-coated gold particles, putative transformants
able to utilize nitrate as a nitrogen source were recovered with an efficiency
of approximate to 2.5 x 10(-5). DNA analysis indicated that the plasmid
integrated into the genome, often in multiple copies, at sites other than the nitA locus. Cotransformants were
recovered with a frequency of 40-80% when cells were cobombarded
with a selected and an unselected marker. Thus, V. carteri
becomes one of the simplest multicellular organisms
that is accessible to detailed molecular studies of
genes regulating cellular differentiation and morphogenesis.
KOUFOPANOU V
THE EVOLUTION
OF SOMA IN THE VOLVOCALES
AM NAT 143 (5): 907-931 MAY 1994
Abstract:
The presence of soma and the manner in which it segregates from the germ line
is a fundamental aspect of development. This article examines the origin and
evolution of soma in the Volvocales, the flagellated
forms of green algae by analyzing data on cell division and development of 370
species. Phylogenetic analysis suggests that the cell
wall is a preadaptation for the evolution of large multicellular colonies with deterministic development. The allometry of soma and germ supports the idea that soma
functions to provide functional flagella during the embryogenesis of large
colonies (Volvocaceae). The need for soma arises from
a constraint that prevents simultaneous flagellation and cell division of cells
surrounded by rigid walls: basal bodies cannot remain attached to their
flagella while migrating to the mitotic poles. The con-straint
is different from those that may cause the separation of flagellation and cell
division in metazoan cells. Apart from a few developmental variations, which
may represent adaptations to larger size, the Volvocaceae
can be obtained by heterochronic changes in the
timing of cell division. Their small size compared to the size of nonflagellated relatives can be attributed to their
locomotion by flagella, which limits the maximum amount of germ that can be
carried by the soma. This limitation is manifested in a negative correlation
between size and number of germ cells among the largest species of Volvocaceae (Volvox). the opposite of a positive one among the smaller species.
NOZAKI H, ITOH M
PHYLOGENETIC-RELATIONSHIPS
WITHIN THE COLONIAL VOLVOCALES (CHLOROPHYTA) INFERRED FROM CLADISTIC-ANALYSIS
BASED ON MORPHOLOGICAL DATA
J PHYCOL 30 (2): 353-365 APR 1994
Abstract:
A cladistic analysis was used to deduce the phylogenetic relationships within the colonial Volvocales. Forty-one pairs of characters related to gross morphology and ultrastructure of vegetative colonies as well as asexual and sexual reproduction were analyzed based on parsimony, using the PAUP 3.0 computer program, for 25 species belonging to nine volvocacean and goniacean genera of the colonial Volvocales. Chlamydomonas reinhardtii Dangeard was the outgroup. The strict consensus tree indicated the presence of two monophyletic groups, one composed of all the volvocacean species analyzed in this study and the other containing the goniacean species except for the four-celled species Gonium sociale (Dujardin) Warming. In addition, these two groups constitute a large monophyletic group, to which G. sociale is a sister group. A new combination Tetrabaena socialis (Dujardin) Nozaki et Itoh and a new family Tetrabaenaceae Nozaki et Itoh are thus proposed for G. sociale. In addition, the analysis suggests that the volvocacean genera Eudorina and Pleodorina are paraphyletic groups, respectively, and that the monotypic genus Yamagishiella has no autapomorphic characters and represents primitive features of the anisogamous and oogamous genera of the Volvocaceae. Phylogenetic relationships within the Volvocaceae and the Goniaceae, as well as the various modes of sexual reproduction exhibited by these organisms, are discussed on the basis of the analysis.
HALLMANN A, SUMPER M
AN INDUCIBLE
ARYLSULFATASE OF VOLVOX-CARTERI
WITH PROPERTIES SUITABLE FOR A REPORTER-GENE SYSTEM - PURIFICATION,
CHARACTERIZATION AND MOLECULAR-CLONING
EUR J BIOCHEM 221 (1): 143-150 APR 1 1994
Abstract:
The multicellular green flagellate Volvox carteri synthesizes
a periplasmic arylsulfatase
in response to sulfur deprivation. The inducible enzyme has been purified to
homogeneity and characterized. The corresponding gene and cDNA
have been cloned. Determination of the sequence of genomic clones and
comparisons to the cDNA sequence, revealed sixteen introns and seventeen a exons that encode a 649-amino-acid polypeptide chain. Since
the arylsulfatase enzyme is readily assayed using chromogenic substrates, but is not detectable in cells
grown in sulfate-containing medium, the gene encoding arylsulfatase
may be useful as a reporter gene in V. carteri. In
addition, the highly regulated promoter of the arylsulfatase
gene suggests its suitability as a tool for producing inducible expression
vectors for cloned genes.
SEKIMOTO H, SONE Y, FUJII T
REGULATION OF
EXPRESSION OF THE GENES FOR A SEX-PHEROMONE BY AN INDUCER OF THE SEX-PHEROMONE
IN THE CLOSTERIUM PERACEROSUM-STRIGOSUM-LITTORALE COMPLEX
PLANTA 193 (1): 137-144 MAR 1994
Abstract:
A sex pheromone, protoplast-release-inducing protein (PR-IP), of the Closterium peracerosum-strigosum-littorale
complex is known to induce the release of protoplasts from mating-type minus
(Mt(-)) cells during sexual reproduction and to have two subunit polypeptides
of 19 and 42 kDa. Here, we describe the regulation
mechanism for the release of the PR-IP. The sex pheromone was fractionated to
yield subunits of 19 and 42 kDa, respectively, and
each subunit was treated with V8 protease and with CNBr.
By reference to the partial amino-acid sequences of the digested polypeptides, oligo nucleotides were synthesized and used as primers for
the combined reverse transcription-polymerase chain reaction. Amplified
fragments of DNA, of 130 bp in the case of the 19-kDa
subunit and of 330 bp in the case of the 42-kDa
subunit, were obtained, sequenced, and used as probes to identify the
respective transcripts. From the results of Northern hybridization, the sizes
of transcripts were estimated to be 1.2 kb for the 18-kDa subunit and 1.4 kb
for the 42-kDa subunit. These transcripts appeared transiently only when
mating-type plus (mt(+)) cells were treated with another sex pheromone (PR-IP
Inducer) for more than 4h in the light. By immunoblotting
with anti-42-kDa-subunit antiserum, it was shown that PR-IP accumulated
gradually in the medium but not in the mt(+) cells after treatment with PR-IP Inducer in the light.
We suggest that PR-IP is synthesized de novo and secreted from mt(+)
cells only after the perception of PR-IP Inducer that has been released from mt(-) cells in the light during the sexual reproduction of Closterium, An analysis by genomic Southern hybridization
revealed that probes for the 19-kDa and 42-kDa peptides hybridized to 6.8-kb and
5.1-kb DNA fragments, respectively, after the digestion of the genome with EcoRI. These hybridized DNA fragments were obtained not
only from the genome of mt(+) cells but also from the genome of mt(-)
cells, in which no transcripts for PR-IP could be detected by Northern
hybridization. On the basis of these results, we discuss the possibility that
the expression of the gene for the two subunits of PR-IP might be critically
dependent upon the action of putative sex-determining genes.
SCHIEDLMEIER B, SCHMITT R
REPETITIOUS
STRUCTURE AND TRANSCRIPTION CONTROL OF A POLYUBIQUITIN GENE IN VOLVOX-CARTERI
CURR GENET 25 (2): 169-177 FEB 1994
Abstract:
Southern analysis indicated the presence of at least four ubiquitin
gene loci in the Volvox carteri
genome. Three of these, a polyubiquitin gene
described here and a non-segregating ubiquitin gene
pair, were assigned to two different linkage groups by RFLP mapping; the
non-polymorphic fourth gene locus remained unassigned. The polyubiquitin
gene was cloned and its 2,116-bp sequence determined. It contains six exons each interrupted by an intron
at Gly35, and it encodes a pentameric polyubiquitin polypeptide consisting of five runs of 76
identical amino-acid residues and a C-terminal extension of one leucine. The five tandem repeats of coding units plus introns exhibit an unusually high degree of overall
sequence identity indicating an efficient process of gene homogenization in
this region of the V. carteri genome. S1 mapping
revealed two closely-spaced transcription starts, 24 and 28 nucleotides
downstream from a putative TATA sequence. Preceding the TATA box are two 14-bp
conserved heat-shock elements (HSEs) and two octameric sequences closely resembling an
yeast HSE. Consistent with a 1.6-kb transcript seen on Northern blots are two polyadenylation signals (TGTAA) located 99 bp and 169 bp downstream from the
TGA translational stop. The polyubiquitin gene was
transcribed throughout the Volvox life cycle
with peaks in the 1.6-kb mRNA levels during pre-cleavage, cleavage, and
post-inversion. In contrast, an 0.6-kb monoubiquitin transcript was abundant only at the
pre-cleavage stage suggesting a different type of gene control. Heat shock
increased the level of polyubiquitin mRNA, whereas
the level of monoubiquitin mRNA was down-regulated.