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 rates of hydrolysis of homopolyribonucleotides to be a preference for
guanine base. The complete amino acid sequence of
RNase NW was deduced by a combination of
protein and
cDNA sequencings. The
cDNA sequence includes the entire coding sequence for a
polypeptide with 229
amino acids including a putative secretion
signal peptide at the N-terminus composed of 25
amino acids. The
amino acids identified by the
protein chemical methods are unambiguously localized within the deduced amino acid sequence from the
cDNA sequence. Comparison of the sequence of
RNase NW 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 present in the style and pollen under normal conditions and is induced in roots in response to
phosphate starvation [Dodds et al., Plant. Mol. Biol., 31, 227-238 (1996)].
RNase NW shows considerable sequence similarity to other known RNases, sharing 57% to 84% identical residues. Northern blot analysis using an
RNase NW cDNA fragment as a probe showed that the
RNase NW transcript was not detected in leaves without wounding, but it was induced within 4 h after wounding and then gradually decreased during 20 h.