Molecular characterization of messenger RNAs for 'pathogenesis related' proteins la, lb and lc, induced by TMV infection of tobacco.

A cDNA library was made to poly(A)-containing RNA from tobacco mosaic virus (TMV)-infected Samsun NN tobacco plants and clones corresponding to mRNAs for the 'pathogenesis-related' (PR) proteins la, lb and lc were identified.One clone was found to contain a complete copy of PR-lb mRNA. The structural organization of this RNA is: a leader sequence of 29 nucleotides, an open reading frame of 504 nucleotides encoding a 30 amino acid long signal peptide and a 138 amino acid long mature protein, and a 3'-non-coding region of 235 nucleotides. Two other clones were found to contain partial copies of PR-la and PR-lc mRNAs. The data indicate an -90% homology between the amino acid sequences of PR-la, -lb and -lc. Using one of the clones as probe it was shown that in the TMV-inoculated lower leaves and the non-inoculated upper leaves of a tobacco plant, the PR-1 mRNAs become detectable from 2 and 8 days after inoculation,respectively.