RESUMEN
The discovery of two nonstandard amino acids, selenocysteine and pyrrolysine, in the genetic code is discussed. These findings have expanded our understanding of the genetic code, since the repertoire of amino acids in the genetic code was supplemented by two novel ones, in addition of the standard 20 amino acids. Current views on specific mechanisms of selenocysteine insertion in forming selenoproteins are considered, as well as the results of studies of new translational components involved in biosynthesis and incorporation of selenocysteine at different stages of translation. Similarity in the strategies of decoding UGA and UAG as codons for respectively selenocysteine and pyrrolysine is discussed. The review also presents evidence on the medical and biological role of selenium and selenoproteins containing selenocysteine as the main biological form of selenium.
Asunto(s)
Código Genético , Lisina/análogos & derivados , Selenocisteína/genética , Animales , Archaea/genética , Archaea/metabolismo , Bacterias/genética , Bacterias/metabolismo , Codón de Terminación , Humanos , Lisina/biosíntesis , Lisina/genética , Biosíntesis de Proteínas , Selenocisteína/biosíntesisRESUMEN
The review summarizes current evidence, including the findings related to molecular phylogeny of ciliates (type Ciliophora) and some related groups of protozoans. Based on comparison of the sequences of genes encoding various ribosomal RNAs (rRNAs), the phylogenetic relationships in seven out of eight known classes of ciliates are discussed. The events related to early branching of the eukaryotic tree are briefly presented. The evolutionary history of amitochondrial protists ids considered with regard to reductionistic evolution and archeozoic hypothesis. The phylogenetic relationships among ciliates and sister groups of apicomplexans and dinoflagellates are considered.
Asunto(s)
Cilióforos/fisiología , Evolución Molecular , Genes de ARNr/fisiología , Filogenia , AnimalesRESUMEN
The review surveys the information, including the most recent data, on the evolution of genetic code in ciliates, which is among the few codes deviating from the universal one. We discuss the cases of recurrent, independently arising deviations from the assignments of standard codons of polypeptide chain termination in the mitochondrial and nuclear genomes of ciliates and some other protozoans. Possible molecular mechanisms are considered, which underlie deviations from standard termination code to coding glutamine (codon UAA and UAG) and cystein or tryptophane (codon UAG) in the nuclear genome. Critical analysis of the main hypotheses on the evolution of secondary deviations from the universal code in ciliates is presented.