THE CODING REGION OF THE SON GENE SMALL TRANSCRIPT CONTAINS 4 AREAS OF PERFECT TANDEM REPEATS

Earlier, cDNA clones of the son gene were isolated by hybridization sc reening of a human embryonic cDNA library using the K51 gene as a prob e [1]. The son gene fragment (1400 bp) present in both the large and s mall transcripts was sequenced [2]. We determined the primary structur e of the small son gene transcript (5675 bp) from human placenta. Its coding region contains four areas of perfect tandem repeats formed by successive duplications. In three of the four analyzed areas the level of amino acid sequence homology of the repeated elements is higher th an the level of nucleotide sequence homology, which indicates the effe ct of natural selection on protein structures encoded by the repeated elements. The finding that natural selection affects amino acid sequen ces suggests that these sequences play an important role in the functi on of the son gene protein product. On the basis of computer analysis data we propose a model for the formation of perfect tandem repeats un der the effect of three factors acting in parallel: DNA duplications, mutational processes in the generated monomers, and natural selection at the level of the son gene protein product.