DNA-binding protein involved in S phase checkpoint control- coupled apoptosis by mediating p53/TP53-induced apoptosis. Has the ability to inhibit DNA synthesis and S phase arrest coupled to apoptosis. Has affinity to both double- and single-stranded DNA. . This is the function of KLLN (killin, p53 regulated DNA replication inhibitor, Ensembl gene identifier ENSG00000227268).