ISOLATION AND CHARACTERIZATION OF A WOUND-INDUCIBLE RIBONUCLEASE FROMNICOTIANA-GLUTINOSA LEAVES

A wound-inducible ribonuclease (RNase NW) was purified from leaves of Nicotiana glutinosa. The purified RNase NW has an optimum pH around 5 and 7, and its base specificity is suggested based on the relative rat es of hydrolysis of homopolyribonucleotides to be a preference for gua nine base. The complete amino acid sequence of RNase NW was deduced by a combination of protein and cDNA sequencings. The CDNA sequence incl udes the entire coding sequence for a polypeptide with 229 amino acids including a putative secretion signal peptide at the N-terminus compo sed of 25 amino acids. The amino acids identified by the protein chemi cal methods are unambiguously localized within the deduced amino acid sequence from the cDNA sequence. Comparison of the sequence of RNase N W with those of other known plant RNases showed that it was identical except for eight residues to that of N. alata RNase NE, which is prese nt in the style and pollen under normal conditions and is induced in r oots in response to phosphate starvation [Dodds et al., Plant. Mol, Bi ol., 31, 227-238 (1996)]. RNase NW shows considerable sequence similar ity to other known RNases, sharing 57% to 84% identical residues, Nort hern blot analysis using an RNase NW cDNA fragment as a probe showed t hat the RNase NW transcript was not detected in leaves without woundin g, but it was induced within 4 h after wounding and then gradually dec reased during 20 h.