DNA replication licensing factor, required for pre-replication complex assembly. Cooperates with cdc6 to promote the loading of the mini-chromosome maintenance complex onto chromatin to form the pre-replication complex necessary to initiate DNA replication. Interacts with pcna. The PIP-box K+4 motif mediates both the interaction with pcna and the recruitment of the DCX(DTL) complex: while the PIP-box interacts with pcna, the presence of the K+4 submotif, recruits the DCX(DTL) complex, leading to its ubiquitination (PubMed:19595719). Ubiquitinated by the DCX(DTL) complex, also named CRL4(CDT2) complex, in response to DNA damage, leading to its degradation. Ubiquitination by the DCX(DTL) complex is necessary to ensure proper cell cycle regulation and is pcna-dependent: interacts with pcna via its PIP-box, while the presence of the containing the 'K+4' motif in the PIP box, recruit the DCX(DTL) complex, leading to its degradation. The interaction with GMNN protects it against ubiquitination. Belongs to the Cdt1 family. Extended N-terminus.