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

Abstract

A guanine nucleotide-specific RNase (RNase Po₁) was isolated from caps of the fruit bodies of Pleurotus ostreatus. RNase Po₁ is most active towards RNA at pH 8.0. The effect of heating on the molar ellipticity at 210 nm of RNase Po₁ showed that RNase Po₁ is more stable than RNase T₁. The primary structure of RNase Po₁ was determined to be<ETGVRSCNCAGRSFTGTDVTNAIRSARAGGSGNYPHVYNNFEGFSFSCTPTFFEFPVFRGSVYSGGSPGADRVIYDQSGRFCACLTHTGAPSTNGFVECRF. It consisted of 101 amino acid residues, with a molecular weight of 10, 760. RNase Po₁ has relatively higher sequence homology with RNase T₁ family RNases. It contains 6 half cystine residues. The locations of four of them are superimposable on those of RNase U₁ and RNase U₂. The amino acid residues forming the active site of RNase T₁ were well conserved in this RNase. Therefore, RNase Po₁ is a unique member of the RNase T₁ family in respect of the location of one disulfide bridge, and its stability.