CLONING AND CHARACTERIZATION OF THE GENE CODING FOR THE HUMAN ACROSOMAL PROTEIN SP-10

SP-10 is a human intra-acrosomal protein that is first detected in the developing acrosome of round spermatids and is observed associated wi th the acrosomal membranes and matrix of mature sperm. Recombinant SP- 10 is currently being tested as a contraceptive vaccine immunogen on t he basis of its tissue specificity as well as functional assays indica ting that anti-SP-10 antisera inhibit sperm-egg interactions. In the p resent study, structural characterization of the human SP-10 gene was undertaken to investigate the expression of the gene and to identify p ossible functions of the SP-10 protein within the acrosome. Genomic bl ots indicate that SP-10 is encoded by a single-copy gene. Mapping and sequencing of the 8-kb SP-10 gene show that the SP-10 mRNA consists of exons of 119, 487, 113, and 390 bp with each exon coding for a distin ct structural domain within the SP-10 protein. An in-frame alternative ly spliced form of the SP-10 mRNA, identified during SP-10 cDNA charac terization, employs the same 3' splice site as the 487-bp exon and a u nique 5' splice site within the 487-bp exon. Previous comparisons of h uman, baboon, and macaque SP-10 cDNA sequences indicated that the babo on and macaque cDNAs contained 60 bp (20 aa) not present in the human SP-10 cDNA. Analysis of the human SP-10 genomic sequence suggests that a 60-bp deletion may have occurred during the evolution of the human SP-10 gene by homologous recombination. This deletion may be responsib le for the reduced level of alternatively spliced SP-10 message presen t within the human testis.