Pyrimidine-specific cleavage by an endoribonuclease of Saccharomyces cerevisiae

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Abstract
An endoribonuclease with pyrimidine cleavage site specificity was isolated from Saccharomyces cerevisiae. The enzyme had a pH optimum of 6 to 7 and did not require a divalent cation. It was inhibited by 5 .times. 10-5 M ethidium bromide, although it appeared to be single strand specific. The enzyme gave a limited cleavage of yeast mRNA and rRNA, yielding products that were terminated with pyrimidine nucleoside 2'',3''-cyclic phosphate. The bonds between pyrimidine and A residues consituted more than 90% of the scission sites when the average product size was 50 nucleotides. Homopolyribonucleotides were cleaved poorly. Poly(A,U) was cleaved rapidly, and analysis of the products of poly(A,U) hydrolysis showed a very stringent cleavage of U-A bonds.