By J. D. WATSON and F. H. C. CRICK
Medial Ruearch C&nclf Unit for the Stud of the llu, wndlsh Molecular structum of Blologlal s labmtory, Cunbrl cr.
HE important of deox@~iuoleio aoid (DNA) within living oelb ia undqmbd . It ia found in 811 dividing oell~, lergelJr if not entirely in the nuoIeus, where it is an eesentieloonetituent of the ohmme aomee. Many lines of evidenoe iadioate that it is tho 08X'Ik Of8 patt Of(ifXlOt ~)thtS@E+Il&iO Spsoifiolty of the ohromommeo end thus of the gene it&f.
May 30, 1953
DNA. /” RASf - SUCAR
\ BASI SUGAR / \ PHosCHATf / BASE-SUGAR CHOSWATf
PnOSPHAIt / RA3f -SUGAR \ PHOIPHATf BASE -sucAR / \ /’
8 oommon fibre exia, 811iaehown diegrammetioelly in Fig. 2. It hae often been 8mumed thet mince there was ody one ohein in the chemio81 fOrmd8 them would OLII~ be one ixi the efruotuml unit. However, the density, teken with the X-rsy evidenoe*, Buggeetn very etrongly th8t there ere two. The other biologiaelly importent f&ure ie the menner in which the two oh8ina are held together. This is done by hydrogen bonds between thebeaee, as ehown aahem8tioelIy in Fig. 3. The beset JIB joined together in p8irs, 8 single bfm from one ahsin being hydrogen-bonded to 8 eingle bese/rom the other. The important point ie th8t only certain pim of baeea will fit into the struoture. One member of 8 p8ir must be 8 purine end the Other 8 mimidine in odor to bridge between the two &bins. If 8 pair oodated of two purines, for exempIe,there would not be room for it. We believe th8t the b8eea will be prerrent 8ho8t ontirely in their meet probable deutomerio forma. If this ie true, the oonditions for forming hydrogen bonds sre mom restrictive, end the only p8ire Of basea possible 8re :
Flg. 2. Thla tklmt b
#rdoltrs the two phapheawns ahnlm. and the heriroaWrodrthspatmdbum holdlog the ahaIm Thevartl~b~laafrlwka
adenine with thymine; gunnine with oytasine.
joined together is shown The w8y in whioh these 81~3 in Fige. 4 8nd 5. A given pir 0811 be either w8y round. Adenine, for ex8mpIe, o8n ooour on either ohain; butqwhen it doea, ita partner on the other IJnt.il now, however, no evidenoe hea been presented be thymine. oh8in mu& 8hvaya to show haw it might 08n-y outthe eesentiel Thie +iring ie strongly supported by the recent operefion required of 8 genetio m8t.43481, that of 8d@8l reeulteh, whioh show that for all sources oxa& eelf&plio8tion. of deoxyribonucleio void eramined the amount of We h8ve moently propoocd 8 etnmturel for the 8denine is olose to the amount of thymine, snd the t+aslt of deoxyribonuoleio said whioh, if aorreot, amount of guenine aloseto the Bmount of oytoeine, immedi8tely sugBosts 8 meohenitml for its self- slthough the oro68-ratio (the r8tio of 8denine to tluplia&ion. X-ray evidence obtained by the workem guanino) can vary from one source to another. 1st King’ College, London*, end presented et the s Indeed, if the sequenoe of ti on one ohei is fame time, gives qu8litetive support to our etruoture irregular, it ia difficult toexplain them 8nalytic81 ad is inoompetible with 8U previously proposed cemdte except by the sort of pairing we have ttt~cturets~. Though the rrtrwtum witl not be com- Sllgtptd. pkttely proved until e mom oxten8ive aomp8rison AMY The phosphate-eugar backbone of our model is been m8de with the X-ray dste, we now feel euffiaient oompletaly reg.&r, but 8ny sequenoe of the peire of coni3denoe in itaenem1 oorreutneaa to di~30u68 its beses a811 fit into the structure. It follows that in 8 genetic81 impiio8tion8. &I doing 80 we 8re1 aeeuming long molecule m8ny different permUtation 8f’ e th8t fibm of the sslt of deoxyribonuoleio ecrid 8re possible, and it therefore seems likely thet the pre~iee not 8rtefaota slicing in the method of pwr8tion, sequence of the baeeg is the code whiuh aerriea the...