The present invention provides a recombinant expression cassette comprising an .alpha.1-3 galactosyltransferase promoter operably linked to a polynucleotide for expression. The invention also provides a recombinant mutating cassette comprising a region of homology to an .alpha.1-3 galactosyltransferase genomic sequence. The cassettes can be employed to express foreign genes or to disrupt the native .alpha.1-3 galactosyltransferase genomic sequence, particularly within an animal. Thus, the invention also provides transgenic animals and methods for their production and use.