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At least 1,153 records · Page 64Linked to original sources
PubMed1969

The rate of molecular evolution considered from the standpoint of population genetics.

The rate of amino acid substitutions in the evolution of homologous proteins is remarkably constant. Furthermore, estimated rates of amino acid substitutions based on comparisons of the alpha hemoglobin chains of various mammals with that of the carp are about the same as those based on comparisons of the carp alpha and mammalian beta or the alpha and beta chains in mammals. These uniformities are regarded as evidence for the hypothesis that a majority of amino acid substitutions that occurred in these proteins are the result of random fixation of selectively neutral or nearly neutral mutations. TWO IMPLICATIONS OF THIS POSSIBILITY ARE DISCUSSED: (a) Random gene frequency drift is playing an important role in determining the genetic structure of biological populations and (b) genes in "living fossils" may be expected to have undergone as many DNA base (and therefore amino acid) substitutions as corresponding genes (proteins) in more rapidly evolving species.

Amino Acid Sequence↗
PubMed1977

Molecular evolution of human and rabbit beta-globin mRNAs.

The primary structures of human and rabbit beta-globin mRNAs are compared. Using as a standard the extent of nucleotide substitutions inferred from the hypervariable amino acid residues of fibrinopeptides A and B, which are thought to change largely by neutral evolution, we show that not all silent mutations in globin mRNA are neutral. The divergence of the sequences is limited in part by the selective usage of synonymous codons. The divergent nucleotides tend to be distributed nonrandomly: in the coding region silent substitutions are most rare in segments that are also deficient in substitutions leading to replacements.

Animals↗
PubMed1979

Molecular evolution of biomembranes: structural equivalents and phylogenetic precursors of sterols.

Derivatives of one triterpene family, the hopane family, are widely distributed in prokaryotes; they may be localized in membranes, playing there the same role as sterols play in eukaryotes, as a result of their similar size, rigidity, and amphiphilic character. Their biosynthesis embodies many primitive features compared to that of sterols and could have evolved toward the latter once aerobic conditions had been established. Membrane reinforcement appears to be achieved in other prokaryotes by other mechanisms, involving either approximately 40-A-long rigid hydrocarbon chains terminated by one polar group acting like a peg through the double-layer or similar chains terminated by two polar groups acting like tie-bars across the membrane. These inserts can be tetraterpenes (e.g., carotenoids). The biophysical function of membrane optimizers appears to have evolved toward sterols by changes limited to only a few enzymatic steps of the same fundamental biosynthetic processes.

Biological Evolution↗
PubMed1983

Molecular evolution of the human adult alpha-globin-like gene region: insertion and deletion of Alu family repeats and non-Alu DNA sequences.

Previous heteroduplex studies have revealed extensive sequence homology between the two human adult alpha-globin-like genes (alpha 2 and alpha 1) and their flanking regions. These homologous regions, which are interrupted by two blocks of nonhomology, each span approximately 4 kilobases [Lauer, J., Shen, C.-K. J. & Maniatis, T. (1980) Cell 20, 119-130]. We have determined 3 kilobases of DNA sequences within and flanking the nonhomologous blocks of these two tandem duplication units. A total of three Alu family repeats has been identified. Two of them are approximately 300 base pairs long and define the 3' ends of the first homology blocks. The third Alu family member is a 600-base-pair-long sequence consisting of two monomeric Alu members arranged in a head-to-tail fashion. It is located in the 3' portion of the first block of nonhomology in alpha 2-gene-containing unit. We present direct evidence that this dimeric Alu sequence was inserted at a staggered break. The second nonhomology block is the result of insertion or deletion of a 224-base-pair sequence. From these data and the calculation of sequence divergence, we propose a history for the evolution of the human adult alpha-globin-like gene region. We also suggest that DNA insertion elements may disrupt gene correction processes in the two duplication units containing alpha 2- and alpha 1-globin genes.

Adult↗
PubMed1988

Gene encoding capsid protein VP1 of foot-and-mouth disease virus: a quasispecies model of molecular evolution.

A phylogenetic tree relating the VP1 gene of 15 isolates of foot-and-mouth disease virus (FMDV) of serotypes A, C, and O has been constructed. The most parsimonious tree shows that FMDV subtypes and isolates within subtypes constitute sets of related, nonidentical genomes, in agreement with a quasispecies mode of evolution of this virus. The average number of nucleotide replacements per site for all possible pairs of VP1 coding segments is higher among representatives of serotype A than serotype C or O. In comparing amino acid sequences, the values of dispersion index (variance/mean value) are greater than 1, with the highest values scored when all sequences are considered. This indicates an accumulation of mutations at a limited number of residues, suggesting that distributions of sequences fluctuate around points of high stability. Evolution of FMDV follows a path very distant from that of a star phylogeny, and it has not been possible to derive conclusions on constancy of evolutionary rates with the test applied to the analysis. FMDVs, as other RNA viruses, are of limited genetic complexity and their population sizes are extremely large. Their evolution concerns complex, indeterminate mixtures of genomes rather than a single, determinate species.

Amino Acids↗
PubMed1988

Directional mutation pressure and neutral molecular evolution.

A quantitative theory of directional mutation pressure proposed in 1962 explained the wide variation of DNA base composition observed among different bacteria and its small heterogeneity within individual bacterial species. The theory was based on the assumption that the effect of mutation on a genome is not random but has a directionality toward higher or lower guanine-plus-cytosine content of DNA, and this pressure generates directional changes more in neutral parts of the genome than in functionally significant parts. Now that DNA sequence data are available, the theory allows the estimation of the extent of neutrality of directional mutation pressure against selection. Newly defined parameters were used in the analysis, and two apparently universal constants were discovered. Analysis of DNA sequence has revealed that practically all organisms are subject to directional mutation pressure. The theory also offers plausible explanations for the large heterogeneity in guanine-plus-cytosine content among different parts of the vertebrate genome.

Animals↗
PubMed1993

Molecular evolution of the myosin family: relationships derived from comparisons of amino acid sequences.

To examine the evolutionary relationships between members of the myosin family, we have used two different phylogenetic methods, distance matrix and maximum parsimony, to analyze all available myosin head sequences. We find that there are at least three equally divergent classes of myosin, demonstrating that the current classification of myosin into only two classes needs to be reexamined. In the myosin II class, smooth muscle myosin is more closely related to nonmuscle myosin than to striated muscle myosin, implying that smooth muscle and skeletal muscle myosins were independently derived from nonmuscle myosin and suggesting that similarities between these types of muscle are the result of convergent evolution. The grouping of head sequences produced by phylogenetic analysis is consistent with classifications based on enzymology and structural localization and is generally consistent with grouping based on common tail structure elements. This result demonstrates that specific head sequences are tightly coupled to specific tail sequences throughout evolution and challenges the idea that myosin heads are freely interchangeable units whose unique function is determined only by the tail structure to which it is attached.

Animals↗
PubMed1994

Molecular evolution of the MyoD family of transcription factors.

Myogenesis in skeletal muscle is a cascade of developmental events whose initiation involves the MyoD family of transcription factors. Evolutionary analyses of amino acid sequences of this family of transcriptional activators suggest that the vertebrate genes MyoD1, myf-5, Myog (myogenin), and myf-6 were derived by gene duplications from a single ancestral gene. A common genetic origin predicts some functional redundancy between MyoD1 and myf-5 and between Myog and myf-6. Experimental studies have suggested that these pairs of genes can substitute for each other during myogenesis. Separate analyses of the conserved basic helix-loop-helix and nonconserved flanking elements yield similar branching sequences but show evolutionary change in the basic helix-loop-helix region has occurred at a much slower rate.

Animals↗
PubMed1987

Molecular evolution and nucleotide sequences of the maize plastid genes for the alpha subunit of CF1 (atpA) and the proteolipid subunit of CF0 (atpH).

The nucleotide sequences of the maize plastid genes for the alpha subunit of CF1 (atpA) and the proteolipid subunit of CF0 (atpH) are presented. The evolution of these genes among higher plants is characterized by a transition mutation bias of about 2:1 and by rates of synonymous and nonsynonymous substitution which are much lower than similar rates for genes from other sources. This is consistent with the notion that the plastid genome is evolving conservatively in primary sequence. Yet, the mode and tempo of sequence evolution of these and other plastid-encoded coupling factor genes are not the same. In particular, higher rates of nonsynonymous substitution in atpE (the gene for the epsilon subunit of CF1) and higher rates of synonymous substitution in atpH in the dicot vs. monocot lineages of higher plants indicate that these sequences are likely subject to different evolutionary constraints in these two lineages. The 5'- and 3'-transcribed flanking regions of atpA and atpH from maize, wheat and tobacco are conserved in size, but contain few putative regulatory elements which are conserved either in their spatial arrangement or sequence complexity. However, these regions likely contain variable numbers of "species-specific" regulatory elements. The present studies thus suggest that the plastid genome is not a passive participant in an evolutionary process governed by a more rapidly changing, readily adaptive, nuclear compartment, but that novel strategies for the coordinate expression of genes in the plastid genome may arise through rapid evolution of the flanking sequences of these genes.

Amino Acid Sequence↗
PubMed1989

Molecular evolution of the telomere-associated MAL loci of Saccharomyces.

The MAL gene family of Saccharomyces consists of five multigene complexes (MAL1, MAL2, MAL3, MAL4, and MAL6) each of which encodes maltose permease (GENE 1), maltase (GENE 2) and the trans-acting MAL-activator (GENE 3). Four of these loci have been mapped and each is located at or near the telomere of a different chromosome. We compare the physical structure of the MAL loci and their flanking sequences. The MAL loci were shown to be both structurally and functionally homologous throughout an approximately 9.0-kb region. The orientation of the MAL loci was determined to be: CENTROMERE . . . GENE 3-GENE 1-GENE 2 . . . TELOMERE. Telomere-adjacent sequences were found flanking GENE 2 of the MAL1, MAL3 and MAL6 loci. No common repeated elements were found on the centromere-proximal side of all the MAL1, loci. These results suggest that, during the evolution of this polygenic family, the MAL loci translocated to different chromosomes via a mechanism that involved the rearrangement(s) of chromosome termini.

Chromosome Mapping↗
PubMed1985

MLS-resistance determinants in Staphylococcus aureus and their molecular evolution.

This paper describes the genetic phenomenology of resistance to macrolide-lincosamide-streptogramin B antibiotics (MLSr) in Staphylococcus aureus and attempts to place this phenomenology in a broad evolutionary context. As antibiotic resistance in general and MLS resistance in particular are typical variable traits in bacteria of clinical interest, we shall begin by introducing the concept of variable genetic traits, as outlined in Figure 1. Variable traits are those that are expressed by some strains of a given species but not by others--in comparison to constant traits which are always present as part of the standard genetic make-up of the species and have constant chromosomal locations. Variable traits are often associated with variable and mobile genetic elements and it is suggested that, in general, they are not likely to have evolved as such in the species in which they are found. Rather, they will most probably have evolved as constant (chromosomal) traits in other species and acquired genetic mobility much later as a rare occurrence in that species. These rarely occurring mobile variants would then spread horizontally within a range of new species. The MLSr determinants in Gram-positive bacteria would appear to represent a classic example of this process. Their remarkable variability will be described as the extant end-point of the process and a probable evolutionary pathway will be traced back to the streptomycetes which are a likely primary source.

Anti-Bacterial Agents↗