Figure 9.

Scheme of TLS.

(A) DNA damage, such as pyrimidine dimers or AP sites, distorts the template structure and prevents replication by the replication-type polymerase.

(B) The stalled replication complex is removed, and a TLS-type polymerase, such as pol ζ, bypasses the damaged site. pol ζ consists of a large catalytic subunit of REV3 and a regulatory subunit of REV7. Opposite the AP site, REV1 inserts a deoxycytidine. This TLS step causes a replication error.

(C) Because of its low processivity, the TLS-type polymerase is replaced by the replication-type polymerase and replication is continued.