Physical Mapping of the Murine Casein Locus Reveals the Gene Order as α-β-γ-ε-κ

Abstract

The murine casein locus has been characterized by long-range restriction mapping and the analysis of large fragment genomic clones. Cloned sequences from five mouse casein genes (α, β, γ, ε, κ) were used to screen a murine (strain 129) genomic library in a bacterial artificial chromosome vector (BAC). Of the nine clones isolated, two contained three casein genes α, α, β, γ and γ, ε, κ, respectively. The following combinations were found in other clones: α + β, β + γ, and γ + ε. Thus, the gene order in the locus can be deduced to be α-β-γ-εκ. This order was confirmed by restriction analysis of the clones. A contig map of the clones and flanking sequences has been established by characterizing seven BAC clones, which together span ∼470 kb. Longrange restriction analysis of genomic DNA indicates that the murine casein locus is confined to a 250-kb partial Xho I fragment. The α and β casein genes were shown to be arranged in a tail-to-tail orientation.