3' end of the malEFG operon in E.coli: localization of the transcription termination site

The nucleotide sequence of a 981 bp's HincII-PvuII DNA fragment containing the 3' end of the malEFG operon in E. coli was determined. This sequence displayed a putative Rho-independent transcription termination site localized 87 bp's after the stop codon of malG. When cloned into plasmid pKG1800, the HincII-PvuII fragment containing this structure acted as a strong transcription termination signal. By S1 mapping, we demonstrated that the 3' end of the malEFG transcript coincided with the putative transcription termination site. One short open reading frames orf1 (123 bp) and and the beginning of another one orf2 were localized after malG. The transcription termination site is localized within orf1. Consequently malG is the last gene of the malEFG operon. orf2 corresponds exactly to the 5' part of the xylE gene reported independently (Davis & Henderson, 1987) as the gene coding for the XylE protein, the xylose-proton symport of Escherichia coli.