Abstract
An 820-nucleotide-long cDNA clone for the kappa-casein (the casein micelle-stabilizing protein) from rat mammary gland was isolated, and its nucleotide sequence was determined. The deduced amino acid sequence from the nucleotide sequence revealed a signal peptide, 21 amino acids long, and a mature protein of 157 amino acids. The signal peptide of rat kappa-casein was highly homologous to that of the precursor to ovine kappa-casein. However, little homology was apparent when the mature kappa-casein protein sequences from ovine or bovine sources were compared with rat kappa-casein. The kappa-casein mRNA content of the mammary tissue was found to increase during its functional differentiation. Prolactin appears to modulate the production of kappa-casein mRNA. Mammary glands of virgin females had no detectable kappa-casein mRNA; however, a marked induction of kappa-casein mRNA was obtained by intravenous infusion of prolactin. Mammary carcinomas did not follow the same pattern. 7,12-Dimethylbenz[a]anthracene-induced mammary carcinomas had normally low levels of kappa-casein mRNA, but intravenous prolactin infusion increased the levels by 2-fold. The MTW9 mammary carcinoma that grows only in the presence of high levels of mammotropic hormones had kappa-casein mRNA content equivalent to that in 10-day lactating rat mammary gland. Continuous venous infusion of prolactin to MTW9 mammary carcinoma did not modify the kappa-casein mRNA levels. Nitrosomethylurea-induced mammary carcinomas had no detectable kappa-casein mRNA, and intravenous prolactin infusion was unable to induce it.
Highlights
An 820-nucleotide-long cDNA clone forthe K-casein casein precipitation in milk, is, important in the from rat mam- process of lactation
Selection of cDNA Clone pK53"Three thousand Tet' and Amp" cDNA clones were generated from an 11-23 S poly(A+) RNA fraction from 14-day lactating rat mammary gland as previously described [17]
The sequencing day lactating rat mammary glandpoly(A+) RNA, and the strategy involved sequencing through the restriction sites
Summary
An 820-nucleotide-long cDNA clone forthe K-casein casein precipitation in milk, is, important in the (the casein micelle-stabilizing protein) from rat mam- process of lactation. The amino acid sequence of the signal mammary carcinoma that grows only in thepresence peptides of rat andovine proteins ishighly conserved whereas of high levels of mammotropic hormones had K-casein mRNA content equivalent to that in 10-day lactating rat mammarygland.Continuousvenousinfusion of prolactin to MTW, mammary carcinoma did notmodify the K-caseinmRNA levels. Preparation of cDNA Clones-Total poly(A+)RNA from14-day lactating rat mammary gland was isolated [14, 15] and fractionated on a neutral sucrose gradient as described [16].
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