The DAZL gene plays an important role in gametogenesis.Microdeletion and mutation of this gene has been frequently associated with the sterility in both vertebrates and invertebrates.Here,a cDNA containing the complete open reading frame of DAZL gene,which encodes putative RRM RNA-binding protein,was isolated from bovine tissues by RT-PCR.The isolated gene was referred to as b-DAZL.Computer-based location analysis showed that b-DAZL is located near the end of chromosome 1.The b-DAZL gene and its vertebrate homologue shared a high nucleotide similarity (90-94%) in the coding region and in the genomic organization,each consisting of 10 exons and 9 introns.Their protein products contained a highly conserved RNA-binding motif,a unique DAZ repeat,and PUM2 and PABP interacting domains.RT-PCR assay revealed that b-DAZL was expressed in the testis and ovary.However,no signals were detected in the testes of sterile male cattle-yaks.The microstructure of the testes of sterile males showed very few spermatocytes but mostly somatic cells.These observations are consistent with the typical phenotype of testes with defective DAZL expression.Subsequent gene detection studies indicated that transcription arrest might lead to a b-DAZL transcript defect in testes of cattle-yaks.Our results suggest that b-DAZL may be involved in spermatogenesis,and that transcription arrest of the gene is associated with male sterility in cattle-yaks.