IN-VIVO STORAGE OF XR FAMILY INTERSPERSED RNA IN XENOPUS OOCYTES

Interspersed RNA is an abundant class of cytoplasmic poly(A)(+) RNA wh ich contains repetitive elements within mostly heterogeneous single co py sequences. In spite of its quantitative importance in oocytes or eg gs (two-thirds of the total poly(A)(+) RNA), very little is known abou t its synthesis, its interaction with other molecules, and its functio nal significance. Here, we analysed a prevalent family of interspersed RNA (XR family) during Xenopus oogenesis. We found that XR interspers ed RNA, unlike extracted interspersed RNA, did not form RNA duplexes i n vivo. In small oocytes (stage III), XR RNA interacted with proteins forming rapidly sedimenting ribonucleoprotein particles (RNPs) with a median sedimentation constant of 80S. However, towards the end of ooge nesis (stage VI), these XR RNPs changed into smaller particles with a median sedimentation constant of 40S. By analysing the proteins associ ated with XR RNA sequence, we have identified a 42 kilodalton protein in small oocytes, which was replaced by a 45 kilodalton protein at sta ge V of oogenesis.