A cDNA encoding K-casein of human milk was cloned and sequenced. The K-casein cDNA was isolated from a λgt11 library generated from mRNA prepared from a mammary gland biopsy obtained from a lactating woman. The library was screened with polyclonal rabbit antibodies raised against purified native K-casein.

The obtained nucleotide sequence contained an ORF sufficient to encode the entire amino acid sequence of a K-casein precursor protein consisting of 182 amino acids. This includes a tentative signal peptide of 20 amino acids and a processed protein of 162 amino acids.