Nucleotide sequence of the promoter region of a tissue-specific human retroposon: comparison with its housekeeping progenitor

The intronless autosomal phosphoglycerate kinase gene (Pgk-2) is a functional retroposon expressed in a tissue-specific manner in the meiotic and postmeiotic stages of mammalian spermatogenesis. The nucleotide sequence of the promoter region of this gene and its transcription start point are compared with those of Pgk-1, an intron-containing, X-linked, housekeeping gene expressed constitutively in all somatic cells and premeiotic germ cells. The location of flanking direct repeats and apparent conservation of specific regulatory sequences suggest the Pgk-2 retroposon arose from reverse transcriptase-mediated processing of an aberrant Pgk-1 transcript that included the endogenous Pgk-1 promoter elements. Specific sequences that may be involved in mediating differences observed in both the level and cell-type specificity of expression of these genes in spermatogenesis are identified.