Zinc ion transporter mediating zinc import from cytoplasm potentially into the endocytic compartment (PubMed:9354792). Controls zinc deposition in milk (PubMed:9354792). Zn(2+)(in) = Zn(2+)(out) Homodimerization could regulate efficiency for zinc transport. Enriched in vesicles within the basal region of epithelial cells. Widely expressed. Highly expressed in the brain and in mammary epithelial cell lines. Defect in Slc30a4 is the cause of the lethal milk (lm) phenotype. Mice with lm are defective in zinc transport into breast milk, due to a premature translation termination codon at position 297. Only homozygous mutant adults develop dermatitis, skin lesions, and hair loss due to a systemic zinc deficiency. Pups of any genotype suckled on homozygous mutant female also develop symptoms characteristic of nutritional zinc deficiency, including dermatitis, alopecia and stunted growth. Belongs to the cation diffusion facilitator (CDF) transporter (TC 2.A.4) family. SLC30A subfamily.