Inactivation of germ-cell-specific molecules essential for the production of functional spermatozoa could lead to attractive new means for male contraception. The mouse protein MSY2 is the mammalian homologue of a class of Xenopus DNA/RNA-binding proteins needed for the transcription of testis-specific genes and for translational repression (masking) of paternal mRNAs. In this report, we describe the human homologue for MSY2, Contrin. Sequence analysis of Contrin cDNAs predicts a protein highly similar to its mouse and Xenopus germ-cell Y-box protein homologues with a cold shock domain and four basic/aromatic islands. Contrin is highly basic and is rich in the amino acids arginine and proline. It contains seven putative casein kinase 2 phosphorylation sites and three putative protein kinase C phosphorylation sites, suggesting that Contrin could be highly phosphorylated in vivo. The predicted protein sequence contains two nuclear localization signals, consistent with its predicted role of shuttling between nucleus and cytoplasm. Contrin maps to human chromosome 17p11.2-13.1. By the criteria of northern and western blotting, Contrin appears to be testis specific and distinct from other mammalian Y-box-binding proteins. We predict that inactivation of Contrin function in mammalian germ cells would prevent the formation of functional male gametes.