Expression of the sulfonamide resistance gene from plasmid R46

The expression of the sul I gene from plasmid R46, a wide host range plasmid of the IncN incompatibility group, was studied in Escherichia coli. Using a promoter test vector, a promoter was detected upstream of the sul I gene. From a nuclease protection experiment, the transcription was determined to start 360 bp upstream of the coding sequence. Two putative promoter -35 and -10 sequences were found upstream from the predicted transcription start. The presence of this promoter sequence in other R factors was discussed in relation with previous data showing that the sul I genes were transcribed from other promoters. The translation product of the sul I gene was detected in minicells. Its size indicates that the translation starts at the first ATG codon found in the open reading frame.