Translesion synthesis(TLS) is a mechanism of DNA damage tolerance in cells,which can be divided into two categories: error-free TLS and error-prone TLS. Human polymerase eta( Pol eta) is one of translesion synthesis DNA polymerases. This protein exhibits lower fidelity and processivity than replicative DNA polymerases. In addition, it possesses "action-at-a-distance" and reverse transcriptase activity. Human Pol eta has the ability to catalyze error-free TLS and error-prone TSL, and may be involved in somatic hypermutation of immunoglobulin variable genes.