摘要：

Aribonuclease (RNase) activity, RNase"XlaI," responsible fortheexcision of intervening sequences fromtwoyeast transfer ribonucleic acid (tRNA)precursors, pre-tRNA"yr andpreAtRNA3Leu, hasbeenpurified 54-fold fromnuclear extracts of Xenopus laevis oocytes. TheRNasepreparation isessentially freeofcontaminating RNase.A quantitative assayforRNaseXlaIwasdeveloped, andthe reaction products werecharacterized. RNaseXlaIcleavage sites intheyeast tRNAprecursors wereidentical tothose madebyyeast extracts (including 3'phosphate and5'-hydroxyl termini). Cleavage ofpreAtRNA3?lu byRNaseXlaI andsubsequent ligation ofthehalf-tRNA molecules donotrequire removal of the5'leader or3'trailer sequences. Thediscovery ofintervening sequences (IVSs) hasledtoareformulation oftheinformational processing pathway ineucaryotes (9,10,12). Thefirst caseofanIVSinatRNAgenewas that described byGoodmanandco-workers (13) inyeasts. Theintervening sequences inyeast transfer ribonucleic acids (tRNA's) werefound tobepost-transcripti onally

展开