E3 ubiquitin-protein ligase that functions in the antephase checkpoint by actively delaying passage into mitosis in response to microtubule poisons. Acts in early prophase before chromosome condensation, when the centrosome move apart from each other along the periphery of the nucleus. Probably involved in signaling the presence of mitotic stress caused by microtubule poisons by mediating the 'Lys- 48'-linked ubiquitination of target proteins, leading to their degradation by the proteasome. Promotes the ubiquitination and subsequent degradation of AURKA and PLK1. Probably acts as a tumor suppressor, possibly by mediating the polyubiquitination of HDAC1, leading to its degradation. May also promote the formation of 'Lys-63'- linked polyubiquitin chains and functions with the specific ubiquitin- conjugating UBC13-MMS2 (UBE2N-UBE2V2) heterodimer. Substrates that are polyubiquitinated at 'Lys-63' are usually not targeted for degradation, but are rather involved in signaling cellular stress. {ECO:0000269|PubMed:10935642, ECO:0000269|PubMed:11807090, ECO:0000269|PubMed:11912157, ECO:0000269|PubMed:14562038, ECO:0000269|PubMed:14694445, ECO:0000269|PubMed:18172500, ECO:0000269|PubMed:19182791}. This is the function of Ensembl gene identifier ENSG00000072609 (CHFR, checkpoint with forkhead and ring finger domains).