CRTJ FOUND TO DISTANT BINDING-SITES INTERACTS COOPERATIVELY TO AEROBICALLY REPRESS PHOTOPIGMENT BIOSYNTHESIS AND LIGHT-HARVESTING-II GENE-EXPRESSION IN RHODOBACTER-CAPSULATUS

Expression of light harvesting II genes and of bacteriochlorophyll and carotenoid biosynthesis genes in Rhodobacter capsulatus is repressed under aerobic growth conditions by the transcription factor CrtJ. In t his study, we demonstrate that the crtA-crtI intergenic region contain s divergent promoters that initiate transcription 116 base pairs apart , based on primer extension analyses. DNase I protection assays demons trate that purified CrtJ binds to one palindrome that overlaps the crt A -10 promoter recognition sequence as well as to a second palindrome that overlaps the -35 crtI promoter recognition sequence. Similar anal yses also show that the puc promoter region contains two distant CrtJ palindromes, with one near the -35 promoter recognition sequence and t he other located 240 base pairs upstream. Gel mobility shift and filte r retention assays indicate that CrtJ binds in a cooperative manner to these distantly separated palindromes. In vivo expression assays with puc and crtI promoter reporter plasmids further demonstrate that aero bic repression of puc and crtI expression requires both CrtJ palindrom es. These in vitro and in vivo results indicate that aerobic repressio n of puc, crtA, and crtI expression involves cooperative interactions between CrtJ bound to distant palindromes. A DNA looping model is disc ussed.