Evidence that the PERF 15 Germ Cell Specific Protein Associates with DNA in the Presence of Ca2+

Metallic ion-mediated interactions between chromosomal proteins and DNA during mammalian spermatogenesis are poorly understood. In search of specific proteins related to this process, we fractionated soluble proteins from rat testis using Ca2 and DNA in low ionic strength solution. A testis specific 16 kDa protein that sedimented in the presence of both Ca2 and DNA was identified as PERF 15 (Swiss-Prot ID: TLBP_RAT) based on amino acid sequence and immunochemical analysis. PERF 15 is the major germ cell protein of the rat perforatorium, but its role during spermatogenesis is unknown. Indirect immunofluorescence showed that PERF 15 was present in the nucleus from spermatocyte to middle spermatid stage. In late-pachytene spermatocytes, PERF 15 colocalized with DNA. In addition, PERF 15 contained phosphotyrosine like other fatty acid binding proteins with high similarity. These results suggest that PERF 15 specifically associates with germ cell chromatin and that its function may be regulated by Ca2 and tyrosine phosphorylation.