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SUPERHELICAL TURNS OF CLOSED CIRCULAR DNA IN SOLUTION AND IN A GEL: EVIDENCE FOR A CONFORMATIONAL DIFFERENCE
Author(s) -
Dougherty G
Publication year - 1982
Publication title -
australian journal of experimental biology and medical science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.999
H-Index - 104
eISSN - 1440-1711
pISSN - 0004-945X
DOI - 10.1038/icb.1982.69
Subject(s) - duplex (building) , dna , covalent bond , circular dna , electrophoresis , base pair , value (mathematics) , significant difference , gel electrophoresis , plasmid , crystallography , chemistry , physics , mathematics , chromatography , biochemistry , statistics , quantum mechanics , genome , gene
Summary We have compared the number of superhelical turns, τ, in circular covalently closed plasmid pBRβG DNA obtained by four different methods, each based on one particular distinguishing principle. Three of the methods allow an unequivocal determination of τ under gel electrophoresis conditions, whilst the fourth enables us to determine its value in solution. We were able to detect a significant difference between the two environments, corresponding to an unwinding of the DNA duplex angle by 0·3° when a sample is transferred from solution to gel. The possible existence of such an effect has been generally overlooked by previous investigators. Our result suggests that the previously reported value for the number of base‐pairs per helical turn should be adjusted downwards by about 0·10, so that it applies to conditions in solution.