PREPARATION AND PROPERTIES OF A HYBRID RNASE S' FORMED BY S-PROTEIN AND S-S CONJUGATE OF [NLE-13, CYS-20]S-PEPTIDE WITH 3'-THIOPROPYL(DT)(15)

An analog of the natural S-peptide with Nle and Cys substituted for Me t-13 and Ala-20, respectively, was synthesized by the solid-phase meth od and conjugated with a synthesized 3'-pyridylthiopropyl derivative o f pentadecathymidylate via a disulfide bond, yielding (dT)(15)pO(CH2)( 3)-S-S-[Nle-13, Cys-20]S-peptide. A study of the conformational proper ties of the conjugate revealed that both the peptide and the nucleotid e moieties influenced its secondary structure. It was found that the n ucleotide-peptide conjugate interacts with S-protein to form a functio nal hybrid RNase S'. Kinetic parameters were determined for pyrimidine polyribonucleotide trans-esterification and cyclophosphate hydrolysis by the hybrid RNase S' and its analog lacking a nucleotide domain. Mi nor differences in their capability of cleaving polyribonucleotides an d reduction of k(cat) for cUMP with retention of K-M in the case of th e hybrid enzyme were demonstrated. The hybrid RNase S' was significant ly more efficient in polyadenylic acid cleavage.