The traM gene of the resistance plasmid R1: comparison with the corresponding sequence of the Escherichia coli F factor

Abstract

The 7.7-kb EcoRI fragment of the resistance plasmid R1 contains the gene for the TraM protein. The sequence was identified by the presence of an open reading frame (ORF) which is preceded upstream by two promoter sequences. Both these promoters were found to be active, although the more distant one predominates, as was judged by the relative abundance of mRNA of the expected length. The TraM protein could be synthesized in an in vitro DNA-dependent protein synthesis system if the DNA of the corresponding region was supplied as template. Comparison of the traM genes of R1 and the F factor showed a high degree of similarity, although a number of mutations, especially near the 5' terminus, introduce specific amino acid (aa) changes. Two-thirds of the 3' sequences differ mainly in silent mutations; hence the aa sequence of the corresponding carboxy-terminal portion of the protein is highly conserved. The 5' and 3' untranslated regions of the mRNAs show little homology. One of the promoter regions, the ribosome-binding sequences, and the transcription termination sites are located at comparable positions but differ in details.