Coleman AW, Preparata RM, Mehrotra B, et al.
Derivation of
the secondary structure of the ITS-1 transcript in volvocales and its taxonomic
correlations
PROTIST 149 (2): 135-146 MAY 1998
Abstract:
Knowledge of secondary structure, formed by the gene spacer regions of the
primary transcript of nuclear rDNA cistrons, is lacking for most phyla of
eukaryotes. We have sequenced the first internal transcribed spacer region
(ITS-1) of multiple representatives of the Volvocales, and from comparisons of
these, derived a secondary structure common to the entire group. The secondary
structure model is supported by numerous compensating base pair changes located
within the paired regions of the stem-loops. Within the morphological species,
such as those of Astrephomene and Gonium, the three basal nucleotide
pairs of helices are highly conserved in primary sequence, and the single
stranded region rich in CCAA is identical in sequence, even when isolates come
from all continents of the earth. In other Volvocacean species known to include
many pairs of mating types, this same level of conservation is found to
correlate with the mating subgroups of the species. Thus a comparable degree of
sequence similarity appears to characterize all isolates of a
"biological" species; this is valid for taxonomic species only where
the biological and taxonomic species levels coincide. In addition, the ITS-1
contains information useful for population analyses, and spacer secondary
structure may have additional phylogenetic utility at the level of class or
subclass when that information becomes available for other protistan groups.
Nozaki H, Ohta N, Yamada T, et al.
Characterization
of rbcL group IA introns from two colonial volvocalean species (Chlorophyceae)
PLANT MOL BIOL 37 (1): 77-85 MAY 1998
Abstract:
Group I introns were reported for the first time in the large subunit of
Rubisco (rbcL) genes, using two colonial green algae, Pleodorina californica
and Gonium multicoccum (Volvocales). The rbcL gene of P. californica
contained an intron (PlC intron) of 1320 bp harboring an open reading frame
(ORF). The G. multicoccum rbcL gene had two ORF-lacking introns of 549 (GM1
intron) and 295 (GM2 intron) base pairs. Based on the conserved nucleotide
sequences of the secondary structure, the PlC and GM1 introns were assigned to
group IA2 whereas the GM2 intron belonged to group IA1. Southern hybridization
analyses of nuclear and chloroplast DNAs indicated that such intron-containing
rbcL genes are located in the chloroplast genome. Sequencing RNAs from the two
algae revealed that these introns are spliced out during mRNA maturation. In
addition, the PlC and GM1 introns were inserted in the same position of the
rbcL exons, and phylogenetic analysis of group IA introns indicated a close
phylogenetic relationship between the PlC and GM1 introns within the lineage of
bacteriophage group IA2 introns. However, P. californica and G. multicoccum
occupy distinct clades in the phylogenetic trees of the colonial Volvocales,
and the majority of other colonial volvocalean species do not have such introns
in the rbcL genes. Therefore, these introns might have been recently inserted
in the rbcL genes independently by horizontal transmission by viruses or
bacteriophage.
Haller K, Fabry S
Brefeldin A
affects synthesis and integrity of a eukaryotic flagellum
BIOCHEM BIOPH RES CO 242 (3): 597-601
Abstract:
Eukaryotic flagella and cilia are highly dynamic organelles. In green algae
like Chlamydomonas reinhardtii, flagella absorption and resynthesis is a normal
process during the vegetative cell cycle. Rapid regeneration also occurs after
stress-induced shedding of flagella. Ca2+ ions, protein synthesis, and a kinase
activity are the main factors known to affect resynthesis. Recently, we have
detected that certain small G proteins (Ypt/Rab) and a GTPase regulator (GDP
dissociation inhibitor), known as regulatory elements of intracellular vesicle
transport, are present in flagellar membranes of green algae, raising the
possibility that the organelle's synthesis and/or integrity depends on
functional membrane traffic. In this study, we examined the effect of brefeldin
A (BFA), an inhibitor of intracellular membrane flow and Golgi function in
animal and plant cells, on flagella regeneration in the colonial green alga Gonium
pectorale. We show that low BFA concentrations (<1 mu g/ml) inhibit flagella
outgrowth, while higher amounts cause dose-dependent deflagellation and cell
death. Our findings provide experimental evidence for a direct connection
between intracellular transport and eukaryotic flagella synthesis. (C) 1998
Academic Press.