MBD1(Methyl-CpG-Binding Domain Protein 1), also known as PCM1 or CXXC3, is a protein that in humans is encoded by the MBD1 gene. Using PCR on a hybrid panel and FISH, Hendrich et al.(1999) mapped the MBD1 gene to chromosome 18q21, 2.1 cM distal to MBD2. Using yeast 2-hybrid analysis, reciprocal immunoprecipitation analysis, and protein pull-down assays, Fujita et al.(2003) showed that MBD1 interacted directly with MCAF. Deletion analysis revealed that the C-terminal transcriptional repressor domain(TRD) of MBD1 interacted with a conserved C-terminal domain of MCAF. Reporter gene assays showed that MCAF increased the repressive function of the isolated TRD of MBD1 against SP1. Chromatin immunoprecipitation analysis revealed that MBD1 linked MCAF to methylated promoters. Uchimura et al.(2006) found that MBD1 was multiply sumoylated in HeLa cells. Sumoylation did not alter the intracellular localization of MBD1 at nuclear foci in C-33A human cervical cancer cells.