Characterization of four genes encoding basic proteins of the porcine spermatid nucleus and close linkage of three of them.

Protamines and transition proteins (TNP) play a major role during spermatogenesis and spermatid differentiation. By screening a porcine genomic library with the corresponding cDNAs, we isolated the genomic clones for porcine protamines 1 and 2 as well as for transition proteins 1 and 2. Analysis and comparison of exon-intron structure, 5' and 3' untranslated regions and transcription start points revealed features common to their counterparts in other mammals. In contrast to TNP2 the gene for TNP1 is well conserved among species, indicating a non species-specific function in the chromatin condensation of the spermatid nucleus. Furthermore, Southern blot hybridization of digested phage DNA demonstrated close linkage between both protamine genes and the gene for transition protein 2 in a 13-kb stretch of DNA. Our observations support the hypothesis that these genes may have evolved by gene duplication.