A spectrophotometric method for determination of the modification degrees and molar extinction coefficients for poly(A, epsilonA) and poly(C, epsilonC) copolymers has been developed. Dependence of some absorption and fluorescence parameters of the copolymers on the modification degree has been studied. Distribution of modified residues in copolymers differs from random and depends on modification conditions. Interaction between the TMV protein and copolymers has been investigated. The protein interacts with poly(A, epsilonA) of low or medium modification degree and displays no activity with respect to poly(epsilonA). On the contrary, introduction of epsilonC to the polynucleotide promotes complex formation between poly(C, epsilonC) and TMV protein. Analysis of the fluorescence emission and excitation spectra has revealed energy transfer from tryptophan to epsilonA or epsilon C in the RNP to occur and permits one to estimate the average distance between Trp (presumably Trp 52)o and the RNA base binding region in the virus to be 17 to 20 A.

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