Tobacco and tomato PR proteins homologous to win and pro-hevein lack the "hevein" domain.

Clones corresponding to tobacco pathogenesis-related (PR) proteins PR-4 and tomato PR protein P2 were isolated from phage cDNA libraries of tobacco infected with tobacco mosaic virus and tomato infected with Cladosporium fulvum, respectively. The probe used in these screenings was a polymerase chain reaction product, synthesized on phage DNA from the tobacco cDNA library, using a synthetic oligonucleotide primer whose sequence corresponded to the partial amino acid sequence available for P2. The different cDNA sequences from the tobacco and tomato clones contained open reading frames for small proteins with 80-90% amino acid sequence identity. Both tobacco PR-4 and tomato P2 are synthesized as precursor proteins, with an N-terminal signal peptide involved in extracellular targeting. The proteins are highly similar to putative wound-induced proteins of potato (win) and to the precursor protein of hevein. However, in contrast to the hevein pro-protein and win proteins, PR-4 and P2 do not contain N-terminal, chitin-binding "hevein" domains. The tobacco and tomato genomes contain a limited number of genes corresponding to PR-4 or P2, whose expression is induced upon infection with the above-mentioned pathogens.