Inhibits DNA replication by preventing the incorporation of MCM complex into pre-replication complex (pre-RC) (PubMed:9635433, PubMed:14993212, PubMed:20129055, PubMed:24064211). It is degraded during the mitotic phase of the cell cycle (PubMed:9635433, PubMed:14993212, PubMed:24064211). Its destruction at the metaphase-anaphase transition permits replication in the succeeding cell cycle (PubMed:9635433, PubMed:14993212, PubMed:24064211). Inhibits histone acetyltransferase activity of KAT7/HBO1 in a CDT1-dependent manner, inhibiting histone H4 acetylation and DNA replication licensing (PubMed:20129055). Inhibits the transcriptional activity of a subset of Hox proteins, enrolling them in cell proliferative control (PubMed:22615398). Homotetramer (PubMed:15313623, PubMed:15260975, PubMed:15378034, PubMed:19906994). Interacts with CDT1; this inhibits binding of the MCM complex to origins of replication (PubMed:14993212, PubMed:21543332, PubMed:15260975, PubMed:19906994). The complex with CDT1 exists in two forms, a 'permissive' heterotrimer and an 'inhibitory' heterohexamer (PubMed:14993212, PubMed:15260975, PubMed:19906994). Interacts (via coiled-coil domain) with IDAS (via coiled-coil domain); this targets GMNN to the nucleus (PubMed:21543332). The heterodimer formed by GMNN and MCIDAS has much lower affinity for CDT1 than the GMNN homodimer (PubMed:24064211). Interacts with a subset of Hox proteins, affinity increasing from anterior to posterior types, the strongest interaction being with HOXB1, HOXC9 and HOXD10 (PubMed:22615398). Interacts with LRWD1 from G1/S to mitosis (PubMed:22645314). Mainly cytoplasmic but can be relocalized to the nucleus. Absent during G1 phase, accumulates during S, G2, and M phases, and disappears at the time of the metaphase-anaphase transition. Phosphorylated during mitosis. Phosphorylation at Ser-184 by CK2 results in enhanced binding to Hox proteins and more potent inhibitory effect on Hox transcriptional activity. The disease is caused by variants affecting the gene represented in this entry. Belongs to the geminin family.