Facilitates ubiquitin-independent proteasomal degradation of polycomb protein CBX4 (PubMed:27326929). Plays a role in inhibiting the activity of glucokinase GCK and both glucose-induced and basal insulin secretion (By similarity). Interacts with GCK; the interaction occurs preferentially at low glucose levels. Detected in the nucleus and nucleolus with no expression in the cytoplasm (PubMed:10974535). However, a later study finds expression in the nucleus and cytoplasm with no expression in the nucleolus (PubMed:24187134). Expressed at high levels in brain and liver with significantly lower levels in muscle. Strongly expressed at the mesencephalon (midbrain) of 12.5 dpc embryos.