Discontinuous DNA replication in developing sea urchin embryos

[摘要] Embryosoftheseaurchin,Hemicentrotuspulcherrimus,growingsynchronouslyandenteringthethird“S”phaseat120minafterfertilization,werepulse-labeledwith[3H]thymidineforvariousperiodsrangingfrom15secto20min,andthesizeofnascentDNAwasanalyzedbycentrifugationinanalkalinesucrosegradient.Itwasfoundthatpulse-labelingfor15secgaverisetoasedimentationprofilewithamajorradioactivitypeakatthepositioncorrespondingtoamolecularweightof4×104daltons.One-minuteoflabeling,however,gaveamajorradioactivebandaroundthepositioncorrespondingto1.4×106daltons.Uponincreasingthelabelingtime,theradioactivitypeaksorbandsshiftedtowardtheincreasingmolecularweights.Finally,mostoftheradioactiveDNAwasfoundtosedimentatthebottomwhentheembryoswereexposedto[3H]thymidinefor15minorlonger.ThetimespanoftheSphaseinthecleavageembryoswasabout15min.TheresultsofpulseandchaseexperimentsalsosupportedthediscontinuousmechanismofDNAreplicationinthecleavageembryos.

[学科分类] 生物科学（综合）