We found that DNA polymerase I from Chlamydiophila pneumoniae AR39 (CpDNApoll) presents DNA-dependent DNA polymerase activity, but has no detectable 3'exonuclease activity. CpDNA polI-dependent DNA synthesis was performed using DNA templates carrying different lesions. DNAs containing 2'-deoxyuridine (dU), 2'-deoxymosine (dI) or 2'-deoxy-8-oxo-guanosine (8-oxo-dG) served as templates as effectively as unmodified DNAs for CpDNApoll. Furthermore, the CpDNApolI could bypass natural apurinic/apyrimidinic sites (AP sites), deoxyribose (dR), and synthetic AP site tetrahydrofuran (THF). CpDNApoll could incorporate any dNMPs opposite both of dR and THF with the preference to dAMP-residue. CpDNApolI preferentially extended primer with 3'-dAMP opposite dR during DNA synthesis, however all four primers with various 3'-end nucleosides (dA, dT, dC, and dG) opposite THF could be extended by CpDNApoll. Efficiently bypassing of AP sites by CpDNApoll was hypothetically attributed to lack of 3' exonuclease activity. (c) 2006 Elsevier Inc. All rights reserved.