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1、AStructureforDeoxyriboseNucleicAcidJ.D.WatsonandF.H.C.Crick(1)April25,1953(2),Nature(3),171,737-738Wewishtosuggestastructureforthesaltofdeoxyribosenucleicacid(D.N.A.).Thisstructurehasnovelfeatureswhichareofconsiderablebiologicalinterest.AstructurefornucleicacidhasalreadybeenproposedbyPauling(4)a
2、ndCorey1.Theykindlymadetheirmanuscriptavailabletousinadvanceofpublication.Theirmodelconsistsofthreeintertwinedchains,withthephosphatesnearthefibreaxis,andthebasesontheoutside.Inouropinion,thisstructureisunsatisfactoryfortworeasons:(1)WebelievethatthematerialwhichgivestheX-raydiagramsisthesalt,no
3、tthefreeacid.Withouttheacidichydrogenatomsitisnotclearwhatforceswouldholdthestructuretogether,especiallyasthenegativelychargedphosphatesneartheaxiswillrepeleachother.(2)SomeofthevanderWaalsdistancesappeartobetoosmall.Anotherthree-chainstructurehasalsobeensuggestedbyFraser(inthepress).Inhismodelt
4、hephosphatesareontheoutsideandthebasesontheinside,linkedtogetherbyhydrogenbonds.Thisstructureasdescribedisratherill-defined,andforthisreasonweshallnotcommentonit.Wewishtoputforwardaradicallydifferentstructureforthesaltofdeoxyribosenucleicacid(5).Thisstructurehastwohelicalchainseachcoiledroundthe
5、sameaxis(seediagram).Wehavemadetheusualchemicalassumptions,namely,thateachchainconsistsofphosphatediestergroupsjoiningbeta-D-deoxyribofuranoseresidueswith3',5'linkages.Thetwochains(butnottheirbases)arerelatedbyadyadperpendiculartothefibreaxis.Bothchainsfollowright-handedhelices,butowingtothedyad
6、thesequencesoftheatomsinthetwochainsruninoppositedirections(6).EachchainlooselyresemblesFurberg's2modelNo.1(7);thatis,thebasesareontheinsideofthehelixandthephosphatesontheoutside.TheconfigurationofthesugarandtheatomsnearitisclosetoFurberg's"standardconfiguration,"thesugarbeingroughlyperpendicula
7、rtotheattachedbase.Thereisaresidueoneachevery3.4A.inthez-direction.Wehaveassumedanangleof36°betweenadjacentresiduesinthesamechain,sothatthestructurerepeatsafter10residuesoneachchain,thatis,after34A.Thedistanceofaphosphorusat
