Ovine β-lactoglobulin messenger RNA: Nucleotide sequence and mRNA levels during functional differentiation of the mammary gland

Abstract

The nucleotide sequence of ovine beta-lactoglobulin mRNA has been determined by chemical sequencing of two cDNA recombinant plasmids and primer extension products. Ovine beta-lactoglobulin mRNA consists of a 540 nucleotide coding region, flanked by 39 nucleotide 5' and 206 nucleotide 3' non-coding regions including a 20 nucleotide poly A tail. The deduced 180 amino acid sequence of pre-beta-lactoglobulin is in agreement with the previously published amino acid sequence of signal peptide and mature protein. Northern blot analysis of poly A+ RNAs from the lactating mammary glands of porcine, rabbit and rat species, allowed us to identify a homologous RNA to beta-lactoglobulin mRNA solely in the porcine species. We also detected a mRNA transcript of a size similar to that of beta-lactoglobulin mRNA in hepatic poly A+ RNA from female rat liver treated by estrogens. Furthermore, we have examined the levels of beta-lactoglobulin mRNA during the functional differentiation of the mammary gland and after hormonal stimulation. During the last third of pregnancy, the expression of beta-lactoglobulin gene is significantly more elevated than that of alpha s1- or beta-casein whose mRNA levels were found to change very slightly during this period. Both beta-lactoglobulin and casein mRNAs showed a rapid response and a wide range of change in response to cortisol treatment. However, there was a significant difference in the rate at which these processes occurred, suggesting that beta-lactoglobulin gene expression is regulated independently of the casein genes.