2-COMPONENT RESPONSE REGULATORS FROM ARABIDOPSIS-THALIANA CONTAIN A PUTATIVE DNA-BINDING MOTIF

An expression sequence tag database of higher plants was screened by i n silico profile analysis for response regulators of the two-component regulatory system. Two closely related clones (ARR1 and ARR2), corres ponding to one of the extracted candidates, were isolated from Arabido psis thaliana. The two genes were comparably expressed in all tissues, and at higher levels in the roots. The amino-terminal half of their t ranslation products was highly conserved. This is where a phosphate re ceiver domain with the landmark aspartate residue and a putative DNA-b inding domain were located. Their carboxyl-terminal halves, although l ess similar to each other, included glutamine-rich and proline-rich re gions characteristic of the transcriptional activation domain of eukar yotes. This architecture resembles that of typical bacterial response regulators serving as transcription factors.