[A theoretical analysis of the binding of methyl derivatives of uracil at the contact portion of the active center of ribonuclease S].

In terms of the mechanical model of molecules, a calculation has been carried out of possible positions and binding energies of 1-methyl uracyl in the contact region of the ribonuclease S active site. In the most preferential orientation, 1-methyl uracyl forms hydrogen bonds C(2)=O(uracyl)...H-N(Thr-45), N-H...Ogamma (Thr-45), C(4)=O... ...H-Ogamma (Ser-123). The base position found (atom coordinates are given) is in complete qualitative agreement with the position of the uracyl in UpcA bound to ribonuclease S as revealed by X-ray analysis. The influence studied of methyl substitution in positions 3 and 5 of the pyrimidine cycle on the base orientation within the protein field. It has been shown that the formation of hydrogen bonds with Thr-45 and Ser-123 is not prerequisite for productive fixation of the phosphoribosyl nucleotide moiety in the catalytic region of the enzyme active site.