NUCLEASES OF YEAST .I. PROPERTIES AND VARIABILITY OF RIBONUCLEASES

1. 1.Nucleases are located in both ribosomes and supernatant of the yeast, Saccharomyces fragilis X Saccharomyces dodzhanskii. Ribosomes prepared from either exponentially growing cells or stationary cells exhibit nuclease activity with a pH optimum of around 7 which is not inhibited by 0.02 M EDTA, Polyvinylsulfate inhibits only at high concentrations. Nuclease activity in the 105 000 × g supernatant from exponentially growing cells has a pH optimum of around 8 and is severely inhibited by EDTA and polyvinylsulfate. In contrast, supernant nuclease from stationary cells has a pH optimum of around 6 and is only partially inhibited by EDTA. 2. 2.Supernant nuclear I and II from logarithmic cells have been partially purified. Their pH optimums are 7.4 and 7.6, respectively. Both nucleases are inhibited by EDTA, Zn2+, polyvinylsulfate and phosphate. The inhibition of EDTA is reversed by the addition of Mg2+. Polyribonucleotides are hydrolysed to di- and trioligonucleotides with 5′-phosphomonoester end groups by both nucleases. © 1968.