Molecular evolution of the human Pgk-2 retroposon.
The human phosphoglycerate kinase (Pgk) gene family includes the functional, intronless Pgk-2 gene and the intronless psi hPgk-1 pseudogene, both of which are retroposons of the intron-containing Pgk-1 gene. The divergence of the Pgk-2 retroposon from Pgk-1 is compared with that of the psi hPgk-1 retroposon from Pgk-1 to reveal nucleotide characteristics diagnostic of functional genes. A comparison of the human and mouse Pgk genes indicates that Pgk-2 has evolved more rapidly than Pgk-1 since the two genes diverged early in mammalian evolution, but that the lack of introns in Pgk-2 may have diminished inter-exon variation. The hypothesis that codon bias is related to expression level is shown not to hold for the Pgk genes; however, the idea that a deficiency of TA and CG dinucleotides and an excess of TG and CT dinucleotides contributes to codon bias is supported. Finally, the hypothesis that the Pgk-2 retroposon initially included a copy of the Pgk-1 'housekeeping' promoter and subsequently evolved a tissue-specific promoter is examined and supported. It is concluded that this process involved the loss of the 5' CpG island present in the Pgk-1 gene, and that selection for cell type-specific expression of Pgk-2 at high levels has driven the divergence of this retroposon from its progenitor, Pgk-1.
McCarrey
J R
JR
Division of Reproductive Biology, Johns Hopkins University, School of Hygiene and Public Health, Baltimore, MD 21205.
D000818:Animals; D001483:Base Sequence; D005075:Biological Evolution; D003062:Codon / Q000235:genetics; D004251:DNA Transposable Elements; D005091:Exons; D006801:Humans; D007438:Introns; D051379:Mice; D008969:Molecular Sequence Data; D005810:Multigene Family; D010735:Phosphoglycerate Kinase / Q000235:genetics*; D011401:Promoter Regions, Genetic; D011544:Pseudogenes; D012689:Sequence Homology, Nucleic Acid
D003062:Codon; D004251:DNA Transposable Elements; D010735:Phosphoglycerate Kinase