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The cytoplasmic ribosomal RNAs of Plasmodium spp 总被引:4,自引:0,他引:4
McCutchan TF Li J McConkey GA Rogers MJ Waters AP 《Parasitology today (Personal ed.)》1995,11(4):134-138
Plasmodium spp maintain several structurally distinct sets of ribosomal RNA genes whose expression is developmentally regulated. This feature sets them apart from all other eukaryotes studied to date. In this review, Thomas McCutchan, Jun Li, Glenn McConkey, John Rogers and Andy Waters give an account of the progress in our understanding of this unusual phenomenon as it relates to the biology of the parasite. They also outline an interesting turnabout in scientific direction involving the use of the parasite as an important new model for the study of the eukaryotic ribosome. 相似文献
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Molecular coevolution among cryptically simple expansion segments of eukaryotic 26S/28S rRNAs 总被引:16,自引:4,他引:12
The set of "expansion segments" of any eukaryotic 26S/28S ribosomal RNA
(rRNA) gene is responsible for the bulk of the difference in length between
the prokaryotic 23S rRNA gene and the eukaryotic 26S/28S rRNA gene. The
expansion segments are also responsible for interspecific fluctuations in
length during eukaryotic evolution. They show a consistent bias in base
composition in any species; for example, they are AT rich in Drosophila
melanogaster and GC rich in vertebrate species. Dot-matrix comparisons of
sets of expansion segments reveal high similarities between members of a
set within any 28S rRNA gene of a species, in contrast to the little or
spurious similarity that exists between sets of expansion segments from
distantly related species. Similarities among members of a set of expansion
segments within any 28S rRNA gene cannot be accounted for by their
base-compositional bias alone. In contrast, no significant similarity
exists within a set of "core" segments (regions between expansion segments)
of any 28S rRNA gene, although core segments are conserved between species.
The set of expansion segments of a 26S/28S gene is coevolving as a unit in
each species, at the same time as the family of 28S rRNA genes, as a whole,
is undergoing continual homogenization, making all sets of expansion
segments from all ribosomal DNA (rDNA) arrays in a species similar in
sequence. Analysis of DNA simplicity of 26S/28S rRNA genes shows a direct
correlation between significantly high relative simplicity factors (RSFs)
and sequence similarity among a set of expansion segments. A similar
correlation exists between RSF values, overall rDNA lengths, and the
lengths of individual expansion segments. Such correlations suggest that
most length fluctuations reflect the gain and loss of simple sequence
motifs by slippage-like mechanisms. We discuss the molecular coevolution of
expansion segments, which takes place against a background of slippage-like
and unequal crossing-over mechanisms of turnover that are responsible for
the accumulation of interspecific differences in rDNA sequences.
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Stanley M. Lastick Peter J. Nielsen Edwin H. McConkey 《Molecular & general genetics : MGG》1977,152(3):223-230
Summary HeLa cell ribosomal protein S6, and the increase in its phosphorylation level that occurs after resuspending cells in fresh medium plus serum, were studied using two-dimensional gel electrophoresis. The maximum level of S6 phosphorylation occurs about 2 h after adding fresh medium and serum to cells that have been allowed to grow to high density; this results in an almost complete shift of the spot representing S6 in two-dimensional polyacrylamide gels to a new location. Mixing experiments showed that the differences in the level of phosphorylation occur in vivo and are not an artifact of in vitro sample preparation. This method of stimulating S6 phosporylation provides a convenient system for studying the functional significance of the phenomenon. Only one other ribosomal protein was detectably phosphorylated using [32P]-labeling and autoradiography of dried two-dimensional gels. The level of phosphorylation of this protein, L14, does not change after serum stimulation. 相似文献