ALTERATIONS OF THE PHYSICAL CHARACTERISTICS OF MILK FROM TRANSGENIC MICE PRODUCING BOVINE KAPPA-CASEIN

`kappa-casein is the protein fraction of milk that allows formation of micelles and determines micelle size and function, thus affecting man y of the physical characteristics of milk. Several lines of transgenic mice were generated bearing the B allele of the bovine kappa-CN gene under the control of the regulatory sequences of the caprine beta-CN g ene that specifically directed expression of bovine kappa-CN to the la ctating mammary tissue of these mice. High expression of bovine kappa- CN protein was observed in the lines studied; the total level of prote in in milk was not significantly affected. A high degree of conservati on in the amino acids involved in the predicted three-dimensional stru cture exists between murine and bovine kappa-CN. Milk from transgenic lines expressing high bovine kappa-CN had a significantly smaller mice lle size than did control milk. Therefore, bovine kappa-CN appears to have effectively participated in assembly of murine casein micelles. T here was no effect on the time of rennet coagulation, but the associat ion was significant between the milk of transgenic lines and the produ ction of a stronger curd in rennet-induced gels. We conclude that bovi ne kappa-CN is an appropriate candidate for transgenic technology that would increase the ratio of kappa-CN to the calcium-sensitive caseins , therefore affecting the physical properties of the colloidal casein suspension.