MAPPING OF TRANSCRIPTIONAL START SITES OF THE CEA AND CEI GENES OF THE COLE7 OPERON

Two transcriptional start sites were identified 77 and 78 nucleotides upstream of the translation initiation codon of the colicin E7 gene (c eaE7). The guanosine nucleotide located at the fifth position of the S OS box is probably a universal transcriptional start site of all E gro up colicins. Major and minor transcripts of the immunity gene (cei) ar e initiated at the 3' end of the cea gene. Relative to the - 10 sequen ce, CAAAAT, of the major ceiE7 promoter, the corresponding region of t he cei gene of other E group colicins has an increased content of guan osine nucleotides. However the - 10 sequence of the minor ceiE7 promot er, TATGAT, was found to be conserved in other colicin promoters. The results indicate that the structure of the major promoter of the ceiE7 gene is unique among the E group colicins.