Abstract
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 CSN3, which encodes the B variant. Therefore, a series of 5'-deleted promoter plasmids were constructed to define the core promoter of CSN3. 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 CSN3 in 40 cows. A 2092 bp promoter region of CSN3 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 CSN3 promoter polymorphisms did not correlate with the CSN3 A and B alleles according to the Pearson's chi-square test (p > 0.05). Moreover, the luciferase activity analysis of the CSN3 promoter showed no difference among pGL3 recombinants with different polymorphic CSN3 promoters (p > 0.05). In the genetic selection of dairy cows, mutations in the CSN3 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.