Abstract:
Translation of the mouse protamine 1 (Prm-1) mRNA is repressed for several
days during male germ cell differentiation. With the hope of cloning genes
that regulate the translational repression of Prm-1, we screened male germ
cell cDNA expression libraries with the 3' untranslated region of the
Prm-1 RNA. From this screen we obtained two independent clones that encode
Prbp, a Prm-1 RNA-binding protein. Prbp contains two copies of a
double-stranded-RNA-binding domain. In vitro, the protein binds to a
portion of the Prm-1 3' untranslated region previously shown to be
sufficient for translational repression in transgenic mice, as well as to
poly(I). poly(C). Prbp protein is present in multiple forms in cytoplasmic
extracts prepared from wild-type mouse testes and is absent from testes of
germ cell-deficient mouse mutants, suggesting that Prbp is restricted to
the germ cells of the testis. Immunocytochemical localization confirmed
that Prbp is present in the cytoplasmic compartment of late-stage meiotic
cells and haploid round spermatids. Recombinant Prbp protein inhibits the
translation of multiple mRNAs in a wheat germ lysate, suggesting that Prbp
acts to repress translation in round spermatids. While this protein lacks
complete specificity for Prm-1-containing RNAs in vitro, the properties of
Prbp are consistent with it acting as a general repressor of translation.
