An 18 kb region containing the entire coding sequences of Krt2-6a and Krt-6b, and including 10.5 kb of intervening sequences, was deleted and replaced with an HPRT-neo minigene via homologous recombination. Absence of expression of both genes in homozygous mutant animals was confirmed by RNase protection assay of skin and hair follicles. 1 (J:70812)