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. Homotrimer which circularizes head-to-tail (head is a N-terminus, tail is at C-terminus) to form a toroid. RFC opens the toroid so it can load on DNA. Interacts with both Pol I (pol) and Pol II (polB-polC), with Hel308 (hjm) and with Hjc. Interaction with the C-terminal PIP-box of RfcL may stabilize the toroidal structure. Belongs to the PCNA family.