Molecular aspects of chromatin elimination in Ascaris lumbricoides☆

[摘要] DNAfromspermatids,4-cellstages,andlarvaeofAscarislumbricoideswasisolated,andthegenomesizebeforeandafterchromatineliminationwasdeterminedbyisotopedilution.Accordingtothesedeterminations,27%oftheDNAislostduringtheprocessofchromatinelimination.Thisvalueisbasedontheassumptionthatlarvalnucleiarediploid.ThegenomeswerethencharacterizedbyCsClequilibriumdensitygradientcentrifugationandrenaturationkinetics.TheeliminatedDNAdoesnotdifferfromtheretainedDNAinbasecomposition.About26%oftheDNAof4-cellstageembryossedimentsasalightsatelliteandwasshowntobemitochondrialDNAbyelectronmicroscopy.Renaturationkineticsrevealedthat10%oftheretainedsomaticDNAisrepetitiouswithanaveragefamilysizeof5500to7000copies,whereas90%oftheretainedDNAispresumablycomposedofuniquesequences.Bycontrast,germ-lineDNAcontains23%fastrenaturingDNAwithafamilysizeof7000to10,000copies.Thus,eliminatedDNAconsistsofrepetitiousanduniquesequencesinaratioofabout1:1.HybridizationexperimentsofheterologousrRNAto4-cellstageandlarvalDNAhaveshownthattheeliminatedDNAisnotselectivelyenrichedforribosomalDNA.TheresultsareconsistentwiththeassumptionthateliminatedDNAdoesnotcompriseanyrDNAcistrons.StudieswithcomplementaryRNAindicatethattheeliminatedDNAcontainsrepetitiousDNAsequencesthatarenotpresentinthesomaticrepetitiousDNA.

[学科分类] 生物科学（综合）