px(2), the newly identified gene in Rhizobium leguminosarum, is characterized to enhance its adjacent nodF expression

nodFEL operon is one of the NodD-dependent inducible nod operons that is cl ustered on the symbiosis plasmid of Rhizobium Leguminosarum biovar viciae. A recent study on the upstream regulatory region of nodFEL operon had ident ified a new promoter, which was responsible for the transcription of a 0.72 Kb RNA molecule, called px(2), in the opposite direction to nodF. This new promoter was further characterized to overlap with that of nodF and its in vitro transcription was inhibited by another newly identified nod regulato r, Px. In this paper we report that the sequence analysis of the pr, transc ript revealed only one open reading frame (ORF66), corresponding to a polyp eptide of 66 amino acids. Moreover, the increase in px(2) copy numbers enha nced the in vivo inducible expression level of nodF, whereas the frame-shif t mutation of ORF66 eliminated such effect, providing evidence that px(2) i s responsible for specifically upregulating nodF expression. This result al so raises the big possibility that px(2) encodes this polypeptide. A model for coordinated expression of px(2) and nodF, transcribed divergently from each other, is proposed. (C) 2000 Academic Press.