The function of OBI1 (ORC ubiquitin ligase 1, Ensembl gene identifier ENSG00000152193) is as follows. E3 ubiquitin ligase essential for DNA replication origin activation during S phase (PubMed:31160578). Acts as a replication origin selector which selects the origins to be fired and catalyzes the multi-mono-ubiquitination of a subset of chromatin-bound ORC3 and ORC5 during S-phase (PubMed:31160578). .