Differential accumulation of two size classes of poly(A) associated with messenger RNA during oogenesis in Xenopus laevis☆

摘要

TheRNAoffull-grownoocytesofXenopuslaeviscontainstwodistinctsizeclassesofpoly(A),designatedpoly(A)Sandpoly(A)L,whichcontain15a€“30(mean=20)and40a€“80(mean=61)Aresidues,respectively.Bothpoly(A)Landpoly(A)SareassociatedwithRNAwhichisheterogeneousinsize.Thetwoclassesofpoly(A)+RNAcanbeseparatedbyaffinitychromatography:Onlypoly(A)L+RNAbindstooligo(dT)-celluloseunderappropriateconditions,butupto50%ofthepoly(A)S+RNAcanbeisolatedfromthevoidfractionbybindingtopoly(U)-Sepharose.Bothclassesofpoly(A)+RNAareactiveasmessengerRNAinaninvitrosystemandyieldidenticalpatternsofinvitroproteinproducts.Previtellogenicoocytescontainalmostexclusivelypoly(A)L,whichaccumulatesuptovitellogenesisbutremainsalmostconstantinamount(molecules/oocyte)duringvitellogenesisandinthefull-grownoocyte.Poly(A)Saccumulates(molecules/oocyte)fromearlyvitellogenesisuptothefull-grownoocyte.Thetotalnumberofpoly(A)+RNAmoleculesperoocyteincreasesthroughoutoogenesisfrom2?—1010/previtellogenicoocyte[80a€“90%poly(A)L]to20?—1010/full-grownoocyte(25a€“40%poly(A)L).Itisarguedthatpoly(A)Sisprotectedfromdegradationintheoocyte,thusstabilizingthea€?maternala€?poly(A)+mRNA.