A MOUSE-Y BOX PROTEIN, MSY1, IS ASSOCIATED WITH PATERNAL MESSENGER-RNA IN SPERMATOCYTES

We have isolated a mouse cDNA clone, which encodes the protein MSY1 (m ouse Y box protein 1), a new member of the Y box family of proteins. N orthern analysis indicates that MSY1 mRNA accumulates over 100-fold mo re in testis than in other tissues. Moreover, MSY1 mRNA is development ally regulated, initially appearing at the pachytene stage of spermato genesis. This is the stage of maximal transcription and translation in the spermatocyte. In Xenopus laevis, homologous Y box proteins, FRGY1 and FRGY2, positively regulate transcription from promoters containin g a Y box (CTGATTGGCCAA). In addition, the germ cell-specific Y box pr otein FRGY2 binds maternal mRNA within 60-80 S mRNP storage particles and in doing so regulates translation in the developing oocyte and emb ryo (Smith, L. D., Richter, J. D., and Taylor, M. A. (1984) in Molecul ar Biology of Development (Davidson, E. R., and Firtel, R. A., eds) pp . 129-141, Alan R. Liss, New York). The MSY1 protein can be isolated f rom a 60-80 S mRNP fraction of testis which like the frog oocyte conta ins stored, untranslated mRNAs. Furthermore, cross-linking experiments demonstrate that MSY1 is bound to mRNAs of this fraction. Finally, mo bility shift analysis performed using the isolated protein indicates t hat MSY1 has nucleic acid binding properties similar to those of the F RGY proteins. These data suggest that the mouse Y box protein, MSY1, f unctions similarly to the FRGY2 protein in regulating the storage and translation of germ cell RNAs.