CSN1S1

CSN1S1 is a gene that encodes alpha-S1-casein, one of the major proteins in milk. Alpha-S1-casein is a phosphoprotein that, together with other caseins, forms the casein micelle, a calcium phosphate–bound particle that stabilizes milk and contributes to its nutritional value and dairy functionality, including cheese-making properties.

Genomic context and expression: The CSN1S1 gene is part of a casein gene cluster on chromosome 4 in humans and many other mammals. It contains a signal peptide that directs secretion, and the mature protein is released into milk during lactation. Expression of CSN1S1 is restricted to mammary epithelial cells and is regulated by lactation hormones such as prolactin.

Genetic variation and dairy relevance: In livestock, CSN1S1 shows polymorphism with multiple alleles that influence the amount of alpha-S1-casein in milk and, consequently, overall protein content, calcium content, and coagulation properties important for cheese production. Breeding programs may select for favorable CSN1S1 variants to optimize milk quality and processing characteristics.

Evolution and context: Casein genes, including CSN1S1, are a highly conserved family across mammals and are associated with lactation strategies and milk functionality. They often exhibit species- and population-specific variation that affects milk composition and dairy traits.

See also: Casein, Casein micelle, CSN1S2, CSN2, CSN3.