Germ line cre mediated recombination between the loxP site in Cdkn2btm2Brn and the loxP site in Cdkn2atm1.1Brn deleted a genomic segment encompassing the promoter of Cdkn2b and intron 2 of the Cdkn2a exon 1a. The absence of p15Ink4b, p16Ink4a and p19Arf protein products was confirmed by western blot analysis on mouse embryonic fibroblasts. (J:125189)