EVIDENCE THAT XR FAMILY INTERSPERSED RNA MAY REGULATE TRANSLATION IN XENOPUS OOCYTES

It has been shown that about two thirds of Xenopus oocyte or sea urchi n egg cytoplasmic poly(A)(+) RNA contains interspersed repetitive sequ ences. The functional significance of this interspersed RNA has remain ed unknown. Here the function of a subfamily of interspersed RNA (XR f amily; McGrew and Richter, 1989: Dev Biol 134:267-270) in Xenopus oocy tes was studied. We found that the elimination of T7 XR (one of the tw o complementary strands of the XR repeat) interspersed RNA by compleme ntary oligodeoxynucleotides significantly inhibited protein synthesis. On the other hand, the injection of in vitro synthesized T7 XR RNA st imulated translation. Moreover, the insertion of the T7 XR RNA sequenc e into globin mRNA repressed the translation of the globin mRNA. In or der to explain these results, we analyzed interactions between the XR interspersed RNA and oocyte proteins. We found that the major XR RNA b inding proteins were p56 and p60, which could be the known mRNA ''mask ing'' proteins that bind mRNA and inhibit translation. Further, a 42 k D protein has been identified that appears to bind T7 XR RNA relativel y specifically, although it interacts with mRNA with a lower affinity. Based on all of these data, we have proposed that interspersed RNA ma y be involved in regulating translation by competing with mRNA to inte ract with certain proteins that can regulate translation. (C) 1995 Wil ey-Liss, Inc.