Differential regulation of alpha-lactalbumin and casein messenger RNA's in mammary tissue.

Rat caseins were characterized with respect to moleculare weight and carbohydrate and amino acid content. Messenger RNA was extracted from rat mammary glands at 5, 10, 15, and 20 days of pregnancy and at 2, 8, and 15 days of lactation and translated in a wheat germ cell-free system. Nascent [3H]casein and alpha-[3H]actalbumin were precipitated separately with specific antibodies and identified by their mobilities on sodium dodecyl sulfate:acrylamide gels and by competition with unlabeled casein and alpha-lactalbumin, respectively. Casein messenger rose continuously from Day 5 of pregnancy to Day 15 of lactation. In contrast, alpha-lactalbumin messenger RNA levels remained low during pregnancy but rose markedly during lactation.