Amino acid sequence of the ;pathogenesis-related' leaf protein p14 from viroid-infected tomato reveals a new type of structurally unfamiliar proteins.

We have established the complete sequence of the 130 amino acid residues of the pathogenesis-related (PR) protein p14 accumulating in tomato leaves infected with the viroid of the spindle tuber disease of potato (PSTV) and partial sequences of the PR protein 1a which accumulates in tobacco mosaic virus-infected tobacco leaves. Both PR proteins are closely related to each other. However, no homology could be found between the sequence of p14 and any of the 3061 published protein sequences compiled in the protein sequence database at present. Thus, p14 represents not only the first completely sequenced PR plant protein but also a new type of structurally unfamiliar proteins whose biological function in the diseased plant remains to be elucidated.