Sliding clamp subunit that acts as a moving platform for DNA processing. Responsible for tethering the catalytic subunit of DNA polymerase to DNA during high-speed replication. Unlike its eukaryotic paralog, loads on circular DNA without the replication factor C (RFC) clamp loader, although RFC greatly increases loading efficiency. Stimulates the ATPase activity of replication factor C (RFC) in the presence of ssDNA. Stimulates the helicase activity of Hel308 and may alter its substrate specificity.