STRUCTURE OF THE RABBIT KAPPA-CASEIN ENCODING GENE - EXPRESSION OF THE CLONED GENE IN THE MAMMARY-GLAND OF TRANSGENIC MICE

The rabbit kappa-casein (kappa-Cas) encoding gene has been isolated as a series of overlapping DNA fragments cloned from a rabbit genomic li brary constructed in bacteriophage lambda EMBL3. The clones harboured the 7.5-kb gene flanked by about 2.1 kb upstream and 9 kb downstream s equences. The cloned gene is the most frequently occurring of two kapp a-Cas alleles identified in New Zealand rabbits. Comparison of the cor responding domains in rabbit and bovine kappa-Cas shows that both gene s comprise 5 exons and that the exon/intron boundary positions are con served whereas the introns have diverged considerably. The first three introns are shorter in the rabbit, the second intron showing the grea test difference between the two species: 1.35 kb instead of 5.8 kb in the bovine gene. Repetitive sequence motives reminiscent of the rabbit C type repeat and the complementary inverted C type repeal were ident ified in the fourth and first introns, respectively. Transgenic mice w ere produced by microinjecting into mouse oocytes an isolated genomic DNA fragment which contained the entire kappa-Cas coding region, toget her with 2.1-kb 5' and 4.0-kb 3' flanking region. Expression of transg ene rabbit kappa-Cas mRNA could be detected in the mammary gland of la ctating transgenic mice and the production of rabbit kappa-Cas was det ected in milk using species-specific antibodies. The cloned gene is th us functional.