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

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 X araino add sequence homoiogy to the known addle pathogenesisrelated (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-la gene; the two other clones do not correspond to known THV-1nduced PR-1 mRNA's and may represent silent genes. Compared to the PR-la gene, these genes contain an Insertion or deletion 1n the putative promoter region and mutations affecting the PR-1 reading frame.