Structure and expression of the mouse casein gene locus

The analysis of yeast artificial chromosomes (YACs) containing the complete mouse casein gene locus revealed the presence of five casein genes, α -, s-, γ -, δ-, and κ-casein, in this order, in the locus. The a- and s-casein genes are only 10 kb apart and have convergent transcriptional orientations. The distance between the s-casein gene and the αs2-like γ-casein gene is about 70 kb, and these genes have divergent transcriptional orientations. The γ - and δ-casein genes, both encoding a αs2-like casein, are linked within 60 kb and convergently transcribed. The κ-casein gene is located about 100 kb from the δ-gene. Except for the presence of the δ-casein gene, the organization of the mouse casein locus resembles that of the bovine locus, including the transcriptional orientation of the genes. In contrast to the other casein genes, which are strongly induced at mid-lactation, expression of the 8-casein gene is abruptly induced upon parturition. Comparative analysis of αs2-like sequences from various species suggests that the ancestral αs2-like gene duplicated around the time of radiation of the rodent and artiodactylid ancestors.