Sensor of abasic sites in single-stranded DNA (ssDNA) required to preserve genome integrity by promoting error-free repair of abasic sites (PubMed:30554877). Recognizes and binds abasic sites in ssDNA at replication forks and chemically modifies the lesion by forming a covalent cross-link with DNA: forms a stable thiazolidine linkage between a ring-opened abasic site and the alpha-amino and sulfhydryl substituents of its N-terminal catalytic cysteine residue (PubMed:30554877, PubMed:31235915, PubMed:31504793). May act as a protease: mediates autocatalytic processing of its N-terminal methionine in order to expose the catalytic cysteine (By similarity). Glu-105 is involved in sensing abasic sites in single-stranded DNA (ssDNA) (PubMed:31504793). His-160 stabilizes the abasic sites by forming a hydrogen bond with the O4' hydroxyl group (PubMed:31235915). The thiol group of the catalytic Cys-2 is deprotonated by its alpha-amino group to form a thiolate anion that is poised for catalysis (PubMed:31504793). The abasic site sugar moiety is in equilibrium between its cyclic furanose and open-chain aldehyde forms (PubMed:31504793). The Cys-2 thiolate anion attacks the abasic site C1' position to form a covalent bond (PubMed:31504793). The Cys-2 alpha-amino group proton then transfers to the oxygen which is stabilized by the Asn-75 side chain (PubMed:31504793). The O4' rotates to a new position and interacts with the His-160 side chain (PubMed:31504793). The Cys-2 alpha-amino group then attacks the C1' position and transfers a proton to the hydroxyl group to release a water molecule, meanwhile forming a covalent bond with the C1' atom (PubMed:31504793). Thus, a thiazolidine linkage is formed between the abasic site C1' atom and the Cys-2 amino and thiol groups (PubMed:31504793). The Glu-105 side chain carboxyl stabilizes the thiazolidine linkage via a strong hydrogen bond with its amine group (PubMed:31504793). Belongs to the SOS response-associated peptidase family. Was reported to act as an endonuclease that specifically cleaves 5-hydroxymethylcytosine (5hmC)-containing DNA in vitro (PubMed:29020633). Additional experiments are however required to confirm this activity as this protein is present in many organisms that do not utilize methylcytosine for epigenetic control.