PURIFICATION AND PRIMARY STRUCTURE OF A NEW GUANYLIC ACID-SPECIFIC RIBONUCLEASE FROM PLEUROTUS-OSTREATUS

A guanine nucleotide-specific RNase (RNase Po-1) was isolated from cap s of the fruit bodies of Pleurotus ostreatus. RNase Po-1 is most activ e towards RNA at pH 8.0. The effect of heating on the molar ellipticit y at 210 nm of RNase Po-1 showed that RNase Po-1 is more stable than R Nase T-1. The primary structure of RNase Po-1 was determined to be < F EFPVFRGSVYSGGSPGADRVIYDQSGRFCACLTHTGAPSTNGFVECRF. It consisted of 101 amino acid residues, with a molecular weight of 10,760. RNase Po-1 has relatively higher sequence homology with RNase T-1 family RNases. It contains 6 half cystine residues. The locations of four of them are su perimposable on those of RNase U-1 and RNase U-2. The amino acid resid ues forming the active site of RNase T-1 were well conserved in this R Nase. Therefore, RNase Po-1 is a unique member of the RNase T-1 family in respect of the location of one disulfide bridge, and its stability .