Biopolym. Cell. 1986; 2(2):106-111.
Cell Biology
Specific interaction of the cro-repressor with operator site models. Circular dichroism studies
1Kirpichnikov M. P., 1Yartsev A. P., 1Minchenkova L. E., 1Chernov B. K., 1Ivanov V. I.
  1. Institute of Molecular Biology, Academy of Sciences of the USSR
    Moscow, USSR


The circular dichroism (CD) method was used to study the interaction of the crorepressor of the phage A. with a synthetic OR3 operator of 17 base pairs long, and with its 9 base pairs fragment
In both cases addition of cro-protein considerably changed the CD spectra in the region of 260-300 nm. The stoichiometry determined by the CD titration is identical both for OR3 and its fragment: one duplex per cro dimer. The interaction of the cro-protein with non-operator DNAs reveals no visible CD changes at all. The spectral changes during specific interaction are quite different from those for the B-A transition and for winding of the DNA within the B-family towards C-form. A conclusion is drawn that the CD changes are mainly induced by the CD effect in Tyr-26 during specific complex formation, the operator DNA conformation being conserved in a B-like form as a whole.


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