SPECIFIC INITIATION OF TRANSCRIPTION AT A CYANOBACTERIAL PROMOTER WITH RNA-POLYMERASE PURIFIED FROM CALOTHRIX SP PCC-7601

Although in cyanobacteria many genes have been shown to be transcripti onally controlled by specific stimuli, little is known about promoter structure and the form of RNA polymerase that recognizes individual pr omoters. RNA polymerase holoenzyme has been purified from Calothrix sp . PCC 7601. Its polypeptide composition resembles that of the plant ch loroplast enzymes. To study transcription in cyanobacteria further, we have analysed the promoter-recognition properties of the purified enz yme. in vitro transcription was assayed with the promoter of the phyco cyanin gene (cpc1) that is expressed whatever the incident light condi tions. Transcription initiation at the same start point as in vivo was obtained with the Calothrix sp. PCC 7601 purified enzyme and the Esch erichia coil core enzyme supplemented with a Calothrix sp. PCC 7601 si gma factor, but not with the E. coil holoenzyme.