Biopolymers and cell. 1988. Volume 4. № 3. 129 - 133

M. A. Shurdov, A. D. Gruzdev

SUPERHELICAL DNA OF POLYTENE CHROMOSOMES CHIRONOMUS THUMMI

Summary

    The fluorescent micromethod of measurement of DNA superhelical density a in solutions gels o r chromosomes is proposed. EtBr intercalation is used to equalize the EtBr-binding properties of the supercoiled and nicked DNA molecules. The number of 1.84+1.88 left turns of DNA molecule per nucleosome is estimated from the measured value — a=0.094 for the nucleoids of Chironomus thummi polytene chromosomes. Experimental data indicate that about 3-i-6 % of DNA in the nucleoids adopts non-canonical forms when — 0-^:0.06.