Molecular evolution and structure of subunits of nuclear RNA polymerases of eukaryotes in context of the exon-intron organization of their genes

Analysis of literary data (for Saccharomyces cerevisiae, Caenorhabditis ele gans, Arabidopsis thaliana, Home sapiens, and some other Eucarya) and our d ata (for Schizosaccharomyces pombe) on the exon-intron organization of the genes encoding subunits of nuclear RNA polymerases showed that introns in t he orthologous genes from different organisms are arranged nonrandomly, nam ely, their positions, if projected on the map of the comparison of the amin o acid sequences of the orthologous subunits, not infrequently coincide in evolutionarily distant species. As a rule, intron positions correspond to t he boundaries of the structurally conserved regions (domains) or to the sit es of possible turns of the polypeptide chain. For example, introns flank t he secondary structure elements in the Rpb8 subunit with the known three-di mensional structure or the structure-function modules in subunits Rpb10 and Rpc10. These facts are in agreement with the idea of the ancient origin of introns, and with the notion of evolution of ancient::protein sequences th rough the assembly of their genes from short protoexons selected by the nat ure as far back as the RNA world times. Comparative analysis of the Primary structures of the subunits of eukaryotic RNA polymerases allowed us to rev eal a nuclear localization signal in subunit Rpb10 and some hypothetical ar chaeal homologues of subunit Rpc10.