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Results for “Genetic code evolution”

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PubMed1975

A biological role for the major histocompatibility antigens.

A central function of the major histo-compatibility (H) antigens may be to signal changes in self to the immune system. Virus-induced modification of strong transplantation antigens apparently results in recognition by thymus-derived lymphocytes (T cells), with subsequent clonal expansion and immune elimination of cells bearing non-self determinants. The extreme genetic polymorphism found in the major H antigen systems of higher vertebrates may reflect evolutionary pressure exerted by this immunological surveillance mechanism.

Animals↗
PubMed2002

Human demographic history: refining the recent African origin model.

Recent studies of large portions of the human genome support a recent origin of modern humans from an African stock after a bottleneck of moderate size followed by a range expansion out of Africa. Under this simple scenario, patterns of molecular diversity suggest that balancing selection could be more prevalent than positive selection in coding regions.

Africa↗
PubMed1987

Evidence for a type-IV-related collagen in Drosophila melanogaster. Evolutionary constancy of the carboxyl-terminal noncollagenous domain.

Type IV collagen, a major structural component of basement membrane, has been characterized only in vertebrates. It is unique among the collagenous proteins in that it forms specific lattice networks by end-to-end interactions. In particular, in mammals the C-terminal noncollagenous domain (NCl) of collagen IV was shown to be one of the major cross-linking sites in the network assembly. Here, we give the first direct evidence of type-IV-related collagen in invertebrates by sequence analysis of cDNA and genomic DNA clones for the 3'-end of a previously characterized Drosophila collagen gene. The data describe the C-terminal 190 amino acid residues of the triple helix and the entire noncollagenous domain (231 amino acids) of the chain encoded for by this gene. Comparison with data reported for human and mouse alpha 1(IV) chains reveals that triple-helix regions are quite different, while NC1 structures are very similar. This suggests different constraints on triple-helix and NC1 domains during evolution. Present data support the assumption that the NC1 structure originated from duplication of an ancestral sequence; the extent of both interspecies and intramolecular homologies suggests the maintenance in vertebrates and invertebrates of an ancestral specific function.

Animals↗
PubMed2001

On the origin of Ser/Thr kinases in a prokaryote.

The family of Ser/Thr and/or Tyr kinases and that of His kinases play essential roles in signal transduction. For a long time, the former has been found in eukaryotes, the latter in prokaryotes. Studies in the last decade have shown, however, that most bacteria possess from one to more than 10 genes encoding Ser/Thr kinases. This observation raises an important question concerning the evolutionary origin of Ser/Thr kinases found in bacteria. To answer this question, we have analyzed a family of 11 genes encoding Ser/Thr kinases in the cyanobacterium Synechocystis sp. PCC 6803. This bacterium contains the largest number of Ser/Thr kinases among all bacteria whose genomic sequences have been released so far. In this study, we have developed a user-friendly computer program for statistical analysis of codon usages and GC content. The results demonstrate that Ser/Thr kinases have similar codon usages and GC contents as the average of all possible open reading frames (ORFs) deduced from the genome. In contrast, ORFs encoding transposases, as a control in our analysis, display a disparity in both codon usage and GC content, confirming their multiple origin and genetic promiscuity. In light of our results, we propose that Ser/Thr kinases existed before the divergence between prokaryotes and eukaryotes during evolution, or were laterally transferred into prokaryotes at the early stages of bacterial evolution. If Ser/Thr kinases have persisted ever since in prokaryotes under evolutionary pressure, it is then expected that they play important, possibly even essential roles in regulating bacterial activities as do their counterparts in eukaryotes.

Base Composition↗
PubMed2003

Natural selection and the emergence of a mutation phenotype: an update of the evolutionary synthesis considering mechanisms that affect genome variation.

Most descriptions of evolution assume that all mutations are completely random with respect to their potential effects on survival. However, much like other phenotypic variations that affect the survival of the descendants, intrinsic variations in the probability, type, and location of genetic change can feel the pressure of natural selection. From site-specific recombination to changes in polymerase fidelity and repair of DNA damage, an organism's gene products affect what genetic changes occur in its genome. Through the action of natural selection on these gene products, potentially favorable mutations can become more probable than random. With examples from variation in bacterial surface proteins to the vertebrate immune response, it is clear that a great deal of genetic change is better than "random" with respect to its potential effect on survival. Indeed, some potentially useful mutations are so probable that they can be viewed as being encoded implicitly in the genome. An updated evolutionary theory includes emergence, under selective pressure, of genomic information that affects the probability of different classes of mutation, with consequences for genome survival.

Bacteria↗