THE TRAM PROTEIN OF PLASMID-R1 IS A DNA-BINDING PROTEIN

The TraM protein of the resistance plasmid R1 was purified to homogeneity and used for DNA-binding studies. Both gel retardation- and footprint experiments showed that TraM specifically binds to DNA of plasmid R1 comprising the region between the origin of transfer and the traM gene. Several TraM molecules bind and, according to the footprint experiments, two distinct sites of specific binding exist. The two sites are separated from each other by 12 nucleotides and each contains an inverted repeat. DNase I protection assays showed that the initial TraM binding occurs at these palindromic sequences. At higher protein concentrations the lengths of the DNA segments protected by TraM were increased towards the traM gene. In one region this extension leads to binding of TraM protein at its own promoters.