Expanded Substrate Scope of DNA Polymerase theta and DNA Polymerase beta: Lyase Activity on 5'-Overhangs and Clustered Lesions.

作者：Laverty Daniel J; Greenberg Marc M

来源：Biochemistry, 2018.

DOI：10.1021/acs.biochem.8b00911

DNA polymerase theta (Pol theta) is a multifunctional enzyme with double-strand break (DSB) repair, translesion synthesis, and lyase activities. Pol theta lyase activity on ternary substrates containing a 5'-dRP that are produced during base excision repair of abasic sites (AP) is weak compared to that of DNA polymerase beta (Pol beta), a polymerase integrally involved in base excision repair. This led us to explore whether Pol theta utilizes its lyase activity to remove 5'-dRP and incise abasic sites from alternative substrates that might be produced during DNA damage and repair. We found that Pol theta exhibited lyase activity on abasic lesions near DSB termini and on clustered lesions. To calibrate the Pol theta activity, Pol beta reactivity was examined with the same substrates. Pol beta excised 5'-dRP from within a 5'-overhang 80 times faster than did Pol theta. Pol theta and Pol beta also incised AP within clustered lesions but showed opposite preferences with respect to the polarity of the lesions. AP lesions in 5'-overhangs were typically excised by Pol beta 35-50 times faster than those in a duplex substrate but 15-20-fold more slowly than 5'-dRP in a ternary complex. This is the first report of Pol theta exhibiting lyase activity within an unincised strand. These results suggest that bifunctional polymerases may exhibit lyase activity on a greater variety of substrates than previously recognized. A role in DSB repair could potentially be beneficial, while the aberrant activity exhibited on clustered lesions may be deleterious because of their conversion to DSBs.

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