FateofRecipient Deoxyribonucleic AcidDuring Transformation inHaemophilus influenzae

During genetic transformation ofHaemophilus influenzae, segments ofthehost deoxyribonucleic acid(DNA)corresponding totheintegrating donorDNA were degraded andliberated intothemedium.Thisdegradation wasdetected byth. release oftheradioactive label fromhostDNA during atimeperiod matching the timeofdevelopment ofmaximal linkage between donorandhostmarkers. The hostlabel released abovethatreleased fromnontransformed, control cultures was equivalent toabout2% ofthehostgenomeor16X 106daltons ofDNA. The released, labeled material wasacid-soluble anddialyzable. Thelabel release from control cultures wasunaffected at30C;atthistemperature, therecombinationspecific release fromtransformed cells wassuppressed. Highmolecular weight fragments ofhostDNA corresponding insize tothedonorfragments could notbe foundfreewithin thecell, weakly boundtootherhostDNA,orboundtononintegrated donorDNA byareciprocal cross mechanism. Various problems concerning themechanism ofrecombination inbacterial transformation have notbeeninvestigated; amongthese problems is oneinvolving thestate andactivity ofrecipient cell deoxyribonucleic acid(DNA)during integrationofdonortransforming DNA.Morespecifically, theproblem involves thefate ofthose regions oftherecipient cell genomewhichcorrespond directly tothesegments ofdonorDNA being integrated. Theserecombinant regions ofrecipientDNA arefunctionally suppressed ordisplaced inthetransformed cell, since theyare recognized by thenew phenotypic property. Utilizing theHaemophilus influenzae transformationsystem, theexperiments reported herewere designed todetermine whether thefunctional displacement involves aphysical displacement of genomic material. BodmerandGanesan (2), intheir studies on integration inBacillus subtilis transformation, suggested thatgenetically displaced recipient DNA fragments areexcised andexchanged into synapsed donorDNA molecules byareciprocal recombination mechanism. Someinconclusive experimental evidence waspresented insupport of this suggestion. In1965, KentandHotchkiss (8), although citing thesuggestions ofBodmerandGanesan, stated thatthefate offragments ofhostgenome genetically displaced bynewDNA remained un