Purification and Primary Structure of a New Guanylic Acid Specific Ribonuclease from Pleurotus ostreatus

A guanine nucleotide-specific RNase (RNase Po,) was isolated from caps of the fruit bodies of Pleurotus ostreatus. RNase Po, is most active towards RNA at pH 8.0. The effect of heating on the molar ellipticity at 210 nm of RNase Poi showed that RNase Pol is more stable than RNase T,. The primary structure of RNase Po, was determined to be < ETGVRSCNCA-GRSFTGTDVTNAIRSARAGCSGNYPHVYNNFEGFSFSCTPTFFEFPVFRGSVYSGGSPGA-DRVIYDQSGRFCACLTHTGAPSTNGFVECRF. It consisted of 101 amino acid residues, with a molecular weight of 10,760. RNase Poi has relatively higher sequence homology with RNase T, family RNases. It contains 6 half cystine residues. The locations of four of them are superimposable on those of RNase U, and RNase U2. The amino acid residues forming the active site of RNase T, were well conserved in this RNase. Therefore, RNase Po, is a unique member of the RNase T, family in respect of the location of one disulfide bridge, and its stability. Key words: guanylic acid specific ribonuclease, Pleurotus ostreatus, primary structure, purification, ribonuclease. In the fungal world, two types of RNase, RNase T, famil