5S RNA gene specific transcription factor (TFIIIA) changes the linking number of the DNA

The purified 5S gene specific transcription factor A (TFIIIA), when incubated with the relaxed 5S gene in the presence of topoisomerase I alters the conformation of the DNA, resulting in a change in the linking number. This interaction introduces a change of one bp per TFIIIA binding site at a low concentration of DNA to protein (1:2) which increases to an extent of 0.9 turns (9 bp) per TFIIIA binding site at a higher protein concentration (1:12). These analyses support the notion that the binding of TFIIIA to the 5S DNA introduces a minimal change in the topology of circular DNA molecules.