INTRONIC U14 SNORNAS OF XENOPUS-LAEVIS ARE LOCATED IN 2 DIFFERENT PARENT GENES AND CAN BE PROCESSED FROM THEIR INTRONS DURING EARLY OOGENESIS

U14 is a member of the rapidly growing family of intronic small nucleo lar RNAs (snoRNAs) that are involved in pre-rRNA processing and riboso me biogenesis, These snoRNA species are encoded within introns of euka ryotic protein coding genes and are synthesized via an intron processi ng pathway. Characterization of Xenopus laevis U14 snoRNA genes has re vealed that in addition to the anticipated location of U14 within intr ons of the amphibian hsc70 gene (introns 4, 5 and 7), additional intro nic U14 snoRNAs are also found in the ribosomal protein S13 gene (intr ons 3 and 4). U14 is thus far a unique intronic snoRNA in that it is e ncoded within two different parent genes of a single organism. Norther n blot analysis revealed that U14 snoRNAs accumulate during early oocy te development and are rapidly expressed after the mid-blastula transi tion of developing embryos. Microinjection of hsc70 pre-mRNAs into dev eloping oocytes demonstrated that oocytes as early as stages II and II I are capable of processing U14 snoRNA from the pre-mRNA precursor, Th e ability of immature oocytes to process intronic snoRNAs is consisten t with the observed accumulation of U14 during oocyte maturation and t he developmentally regulated synthesis of rRNA during oogenesis.