Structure of tobacco genes encoding pathogenesis-related proteins from the PR-1 group

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Abstract
Infection of Samsun NN tobacco with tobacco mosaic virus (TMV) was found to induce the synthesis of mRNA encoding a basic protein with a 67 % amino acid sequence homology to the known acidic pathogenesis-related (PR) proteins la, lb and lc. By Southern blot hybridization it was shown that the tobacco genome contains at least eight genes for acidic PR-1 proteins and a similar number of genes encoding the basic homologues. Clones corresponding to three of the genes for acidic PR-1 proteins were isolated from a genomic library of Samsun NN tobacco. The nucleotide sequence of these genes and their flanking sequences were determined. One clone was found to correspond to the PR-1a gene; the two other clones do not correspond to known TMV-1nduced PR-1 mRNA's and may represent silent genes. Compared to the PR-1a gene, these genes contain an Insertion or deletion in the putative promoter region and mutations affecting the PR-1 reading frame.