Abstract: Nonexpressor of Pathogenesis-Related Genes1 (NPR1) is a master regulator ofsystemic acquired resistance (SAR). NPR1 is part of a transcription complex mediatingsalicylic acid (SA)-induced expression of Pathogenesis-Related (PR) Protein1 genesthrough co-operation between different proteins. TGA transcription factors link NPR1 tothe PR-1 promoter region, while NIMIN proteins control NPR1 activity. The NPR1 geneis expressed constitutively, and the protein is activated only in response to SA. Fromyeast one-hybrid and yeast two-hybrid analyses, we conclude that the SA signal is likelyto target NPR1 directly. SA signal transduction occurs through two conserved domains inthe C-termini of NPR1 and some NPR1-like proteins. One domain comprises the pentaaminoacid motif LENRV. The other domain comprises the binding site for the SAinducedNIMIN1 and NIMIN2-type proteins.