InterPro domain: IPR002562

This domain is responsible for the 3'-5' exonuclease proofreadingactivity of Escherichia coli DNA polymerase I (polI) and other enzymes, it catalyses the hydrolysis of unpaired or mismatched nucleotides. This domain consists of the amino-terminal half of the Klenow fragment in E. coli polI it is also found in the Werner syndrome helicase (WRN), focus forming activity 1 protein (FFA-1) and ribonuclease D(RNase D) [ 1 ].

Werner syndrome is a human genetic disorder causing premature aging; the WRN protein has helicase activity in the 3'-5' direction [ 2 , 3 ]. The FFA-1 protein is required for formation of a replication foci and also has helicase activity; it is a homologue of the WRN protein [ 4 ]. RNase D is a 3'-5' exonuclease involved in tRNA processing. Also found in this family is the autoantigen PM/Scl thought to be involved in polymyositis-scleroderma overlap syndrome.

1. Replication focus-forming activity 1 and the Werner syndrome gene product. Nat. Genet. 19, 375-8
2. The Werner syndrome protein is a DNA helicase. Nat. Genet. 17, 100-3
3. DNA helicase activity in Werner's syndrome gene product synthesized in a baculovirus system. Nucleic Acids Res. 25, 2973-8