ACTIVATION OF THE CAMV AS-1 CIS-ELEMENT BY SALICYLIC-ACID - DIFFERENTIAL DNA-BINDING OF A FACTOR-RELATED TO TGA1A

Transcription from the as-1 element of the cauliflower mosaic virus is induced by salicylic acid (SA), an endogenous signal involved in plan t defence responses, Electrophoretic mobility shift assays demonstrate d that the binding of a tobacco cellular factor, named SARP, correlate s with the SA-induced activation of transcription. SARP was shown to c ontain proteins immunologically related to TGA1a, a transcription fact or previously cloned for its ability to bind to the as-1 element. The molecular mass of SARP was estimated to be 40 kDa by South-Western exp eriments, Treatment of the extracts with dissociating agents led to an increase in the DNA binding activity, suggesting the presence of an i nhibitor that sequesters SARP, The DNA binding activity appeared sensi tive to phosphatase treatment, suggesting a role for phosphorylation i n the SA-induced gene activation, These results represent an analysis of immediate early response to SA and potentially elucidate the events of the SA signal transduction pathway.