Identification of the Bovine Core Promoter Region and the Relationships Between Promoter Polymorphisms and the A and B Alleles.

Reportedly, the number of κ-casein (κ-CN) B alleles increases the proportion of κ-CN to total protein and the κ-CN content. This phenomenon is caused by single-nucleotide polymorphisms (SNPs) in the promoter region of , which encodes the B variant. Therefore, a series of 5'-deleted promoter plasmids were constructed to define the core promoter of . The promoter activity was analyzed by comparing the luciferase activity among the recombinant vectors with truncated promoters. No mutation occurred in the core promoter region (5'-ctatcgtcagatctttcctttctgtcatcttcctattggtg-3') of in 40 cows. A 2092 bp promoter region of was re-sequenced for detection, and nine variants were found, of which only three variants had mutation frequencies > 40%, which were -1002T>-, -1654T>A, and -2039T>G. The promoter polymorphisms did not correlate with the A and B alleles according to the Pearson's chi-square test ( > 0.05). Moreover, the luciferase activity analysis of the promoter showed no difference among pGL3 recombinants with different polymorphic promoters ( > 0.05). In the genetic selection of dairy cows, mutations in the core promoter should be focused upon. These findings provide a reference for the regulatory mechanism of bovine milk proteins and offer guidance for the genetic selection and breeding of cows.