A MOUSE HOMOLOG OF THE XENOPUS GERM CELL-SPECIFIC RIBONUCLEIC-ACID DEOXYRIBONUCLEIC ACID-BINDING PROTEINS P54 P56 INTERACTS WITH THE PROTAMINE 2 PROMOTER/

Recent evidence indicates that a member of the Y box-binding family of transcriptional regulators is identical to p56, a predominant protein of messenger ribonucleoprotein complexes. The p56 protein is highly e nriched in oocytes and testis, and a functional RNA binding mouse cyto plasmic homologue has been cloned and partially characterized. Because few potential testis-specific transcriptional regulators have been id entified, the testis-enriched Y box-binding proteins represent trans-a cting elements of a unique model system for the study of haploid gene expression. The 5' flanking region of the testis-specific, haploid-exp ressed mouse protamine 2 gene contains an element with a 9-of-12 nucle otide identity with the previously defined Y box consensus sequence. W e have investigated the possible role of Y box-binding proteins in tra nscriptional regulation of protamine 2 using specific antibodies and D NA-protein binding assays. Western blot analyses with two different an ti-p54/p56 antibodies demonstrate that a mouse homologue of Xenopus p5 4/p56 is present in transcriptionally active mouse testis nuclear extr acts. Our results further indicate that the Xenopus Y box-binding prot eins bind to an element 5' to the mouse protamine 2 gene. Similarly, b inding of the mouse testis homologue to the protamine 2 Y box element is demonstrated by gel mobility shift and antibody supershift analyses . The demonstrated interactions between testis-enriched Y box-binding proteins and protamine 2 transcriptional control elements therefore re present a unique system for functional studies to determine the mechan ism of regulation of haploid gene expression.