CELL-SPECIFIC PROTEINS INTERACT WITH THE 3' UNTRANSLATED REGIONS OF PRM-1 AND PRM-2 MESSENGER-RNA

The testis-specific mouse protamine genes (Prm-1 and Prm-2) are transc ribed in haploid round spermatids, their mRNAs stored as cytoplasmic r ibonucleoprotein particles and translated about 1 week later in elonga ting spermatids. We have compared the in, vitro translational efficien cies of deproteinized Prm-1 mRNA isolated from purified populations of germ cells and found that Prm-1 mRNA from round spermatids translates as efficiently as Prm-1 mRNA from elongating spermatids, suggesting t hat translation of Prm-1 mRNA is normally repressed in round spermatid s. Previous studies in transgenic mice have shown that the 3' UTR of P rm-1 mRNA is necessary and sufficient for its translational control (B raun et al., 1989). In this manuscript, we have used an RNA band shift assay to identify an activity, present in cytoplasmic fractions of me iotic spermatocytes and postmeiotic round spermatids, that binds the 3 ' UTRs of both Prm-1 and Prm-2 mRNA. We have used 3' UTR deletion vari ants to map the binding site to a 22-nt region within the Prm-1 3' UTR and to a 20-nt region within the Prm-2 3' UTR, uv cross-linking of th e RNA band shift activities detected with the Prm-1 and Prm-2 3' UTRs generated the same two RNA/protein complexes of 53 and 55 kDa. The pre sence of the binding activity in the cell type and subcellular compart ment associated with Prm-1 and Prm-2 mRNA storage suggest that the act ivity may be actively engaged in translational repression of these mRN As. (C) 1994 Academic Press, Inc.