Abstract : DNA glycosylases are key enzymes in thefirst step of base excision DNA repair, recognizing DNA damage and catalyzingthe release of damaged nucleobases. Bifunctional DNA glycosylases also possess associated apurinic/apyrimidinic (AP)lyase activity that nick the damaged DNA strand at an abasic (or AP) site, formed either spontaneously or at thefirst stepof repair. NEIL1 is a bifunctional DNA glycosylase capable of processing lesions, including AP sites, not only in double-stranded but also in single-stranded DNA. Here, we show that proteins participating in DNA damage response, YB-1 andRPA, affect AP site cleavage by NEIL1. Stimulation of the AP lyase activity of NEIL1 was observed when an AP site waslocated in a 60nt-long double-stranded DNA. Both RPA and YB-1 inhibited AP site cleavage by NEIL1 when the AP sitewas located in single-stranded DNA. Taking into account a direct interaction of YB-1 with the AP site, located in single-stranded DNA, and the high affinity of both YB-1 and RPA for single-stranded DNA, this behavior is presumably aconsequence of a competition with NEIL1 for the DNA substrate. Xeroderma pigmentosum complementation groupC protein (XPC), a key protein of another DNA repair pathway, was shown to interact directly with AP sites but hadno effect on AP site cleavage by NEIL1.
