Transcriptional activator that exhibits a unique DNA binding specificity for CpG unmethylated motifs with a preference for CpGG. Component of the SET1 complex, at least composed of the catalytic subunit (SETD1A or SETD1B), WDR5, WDR82, RBBP5, ASH2L/ASH2, CXXC1/CFP1, HCFC1 and DPY30. Interacts with SETD1A (By similarity). Interacts with ZNF335 (By similarity). Interacts with PRDM9; this interaction does not link PRDM9-activated recombination hotspot sites with DSB machinery and is not required for the hotspot recognition pathway (PubMed:27932493, PubMed:30365547). Interacts with histone H3K4me3 (PubMed:30365547). Associated with euchromatin. During mitosis, excluded from condensed chromosomes (By similarity). Expressed in seminiferous tubules and in both germ cells and Sertoli cells. Highly expressed in spermatogonia, weakly expressed in leptonema and zygonema, and then again high expression in pachynema and diplonema, decreasing to undetectable levels in spermatids. Cxxc1 knockout male mice are fertile. In contrast Cxxc1 germ cell-specific knockout female mice are sterile.