Sequence and structure of cmp, the replication enhancer of the Staphylococcus aureus plasmid pT181

The Staphylococcus aureus plasmid pT181 possesses a DNA replication enhancer element, called cmp, that is required in cis for optimal utilization of the initiator protein by the origin of replication. The minimal nucleotide sequence required for cmp activity was defined by testing progressively smaller DNA fragments for their ability to restore cmp activity in a plasmid mutant deleted for cmp. These experiments indicate that cmp is a sequence of 100 base pairs (bp) characterized by a loosely repeated sequence motif and phased oligo(dT) tracts. Intrinsic DNA bending at cmp was detected by a circular permutation assay of the locus using polyacrylamide-gel electrophoresis and by computer modeling. The cmp element was found to contain two loci of intrinsically bent DNA that confer an overall bent conformation to this replication enhancer.