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Do the two chains of the DNA molecule coil round one another plectonemically! If so. the linking number of relaxed circular DNA containing N base pairs, expected from the classical double helix, should be roughly equal to N/10.pBR322 DNA is a covalently closed circular DNA duplex containing 4362 base pairs. When it is in supereoiled state, its linking number calculated from B-DNA should be of the order of 4×10~2We have determined the linking number or relaxed pBR322 DNA Ⅰ’ with electron microcopy. With the help of gel electrophoresis, it is proved that when DNA Ⅰ’ has the writhing number Wr=2+2, its linking number L=1, 2, 3, 4. A further deduction is that the linking number of native pBR322, Lk《 4362/10.The difference between our experimental results and the estimates from the classical double helix structure is tremendous. The phenomena cannot be explained if there is only one form of DNA structure. Probably the tertiary structure of DNA is intrinsically determined by its primary structure, influen
Do the two chains of the DNA molecule coil round one another plectonemically! If so. The linking number of relaxed circular DNA containing N base pairs, expected from the classical double helix, should be roughly equal to N / 10. pBR322 DNA is a covalently When it is in supereoiled state, its linking number calculated from B-DNA should be of the order of 4 × 10 ~ 2We have determined the linking number or relaxed pBR322 DNA Ⅰ ’with electron microcopy. With the help of gel electrophoresis, it is proved that when DNA I ’has the writhing number Wr = 2 + 2, its linking number L = 1, 2, 3, 4. A further deduction is that the linking number of native pBR322, Lk "4362 / 10. The difference between our experimental results and the estimates from the classical double helix structure is tremendous. The phenomena can not be explained if there is only one form of DNA structure. Probably the tertiary structure of DNA is intrinsically determined by its prima ry structure, influen