Two-component response regulators from Arabidopsis thaliana contain a putative DNA-binding motif

An expression sequence tag database of higher plants was screened by in silico profile analysis for response regulators of the two-component regulatory system. Two closely related clones (ARR1 and ARR2), corresponding to one of the extracted candidates, were isolated from Arabidopsis thaliana. The two genes were comparably expressed in all tissues, and at higher levels in the roots. The amino-terminal half of their translation products was highly conserved. This is where a phosphate receiver domain with the landmark aspartate residue and a putative DNA-binding domain were located. Their carboxyl-terminal halves, although less similar to each other, included glutamine-rich and proline-rich regions characteristic of the transcriptional activation domain of eukaryotes. This architecture resembles that of typical bacterial response regulators serving as transcription factors.