The ribosomal RNA cistrons in clam gametes☆

[摘要] Thelocalization,amplification,andmultiplicityoftherRNAcistronsingametesofthecootclam,Mulinialateralis,havebeeninvestigatedusingisopycniccentrifugationandDNA-RNAhybridization.TherRNAcistronsappeartobelocalizedinahigh-densitysatellitewhichmakesup3–5%oftheDNAinbothgametes.OocyteDNAbinds,ontheaverage,1.6timesasmuchrRNAasdoesspermDNA.ThemitochondrialDNAcomponentofoocytesaccountsfor19%ofthetotalDNA,asestimatedbydenaturationandreannealingfollowedbyisopycniccentrifugation.Hence,theribosomalcistronsareamplifiedabouttwofold(1.60.81)intheseoocytes.ThehaploidMuliniagenomecontainsapproximately120cistronsforrRNA,asmeasuredbyhybridizationwithXenopusrRNAatsaturatingconcentration.TheMuliniaoocytethereforecontainsmanyfewercopiesofrDNAthandoestheoocyteofSpisula,acloselyrelatedspecies,inwhichtheribosomalcistronsexistingreatermultiplicity(195cistrons;Collier,J.R.(1971),Exp.CellRes.69,181–184),andareamplifiedatleastfivefold(Brown,D.D.,andDawid,I.B.(1968),Science160,272–280).SincetheoocytesofthesetwoclamsarethesamesizeandbeginrRNAsynthesisatthesametimeafterfertilization,themagnitudeofrDNAamplificationmustnotbestrictlyrelatedtotheneedsofthedevelopingembryo.

[学科分类] 生物科学（综合）