AbstractThe specific binding ofEscherichia coliRNA polymerase molecules to the DNA of plasmid pNH602, a deletion derivative of R6K having an increased copy number, was detected by electron microscopy. Seven strong RNApol binding sites were found on pNH602 DNA linearized withBamHI orEcoRI restriction endonuclease. All of these specific sites occur in genetically defined regions of the pNH602 molecule. Two of them correspond with the recently reported transcription initiation sites within a region essential for plasmid R6K replication.