Overlap between ampC and frd operons on the Escherichia coli chromosome.

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Abstract
The promoter for the E. coli ampC .beta.-lactamase gene is located within the last gene of the fumarate reductase (frd) operon. Evidence is presented that the ampC attenuator serves as the terminator for transcription of this preceding operon. The nucleotide sequence was determined for 2 proteins that were encoded by a DNA segment preceding the ampC gene. The 2 proteins consisted of 131 and 119 triplets and had MW of 15,000 and 13,100, respectively. The 12 COOH-terminal amino acids of the 13,100 MW protein overlapped the ampC promoter. Accordingly, a G.cntdot.C insertion in the promoter gave both increased transcription of ampC and a frameshift in this overlapping gene, resulting in readthrough proteins. Thus, a type of very compact genetic organization of operons in prokaryotes is described.