POSITIVE AND NEGATIVE REGULATION OF SEQUENCES UPSTREAM OF THE FORM-IICBB CO2 FIXATION OPERON OF RHODOBACTER-SPHAEROIDES

The unlinked form I and form II Calvin cycle CO2 fixation (cbb) operon s of the photosynthetic bacterium Rhodobacter sphaeroides are located on different genetic elements, yet both operons are positively regulat ed by the transcription activator protein CbbR, the product of the cbb R gene located immediately upstream of the form I operon. By employing deletion mutagenesis, and a newly constructed promoter probe vector, the form II operon promoter (cbbF(II)p) and three other promoters (Up, Vp, and Wp) were localized within 2.1 kb upstream of the form II oper on. Mutations in both cbbR and the first gene of the form I operon (cb bF(I)) elicited both positive and negative responses when transcriptio nal fusions controlled by these four promoters were examined. With the exception of Wp, all these upstream promoters were repressed by oxyge n. In addition, these promoters were associated with open reading fram es of unknown function whose deduced amino acid sequences showed no si gnificant relationship to proteins in current databases. The results o f these experiments suggest that the promoter sequences and genes upst ream of the form II cbb operon may be intimately involved with control of the cbb regulon of this photosynthetic organism.