Biopolym. Cell. 1988; 4(3):129-133.
Structure and Function of Biopolymers
Superhelical DNA of polytene chromosomes Chironomus thummi
1Shurdov M. A., 1Gruzdev A. D.
  1. Institute of Cytology and Genetics, Siberian Branch of the Academy of Sciences of the USSR
    Novosibirsk, USSR


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 – σ = 0.094 for the nucleoids of Chironomus thummi polytene chromosomes. Experimental data indicate that about 3÷6 % of DNA in the nucleoids adopts non-canonical forms when – σ>0.06.


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