A targeting construct where exons 2-10 of Psme1 were replaced with a neomycin resistant cassette and exons 2-10 of Psme2 were deleted was used to disrupt both loci in a single homologous recombination event. The sequence of Cgi112 (1500005A01Rik), the gene located between Psme1 and Psme2, remained unchanged. Northern blot and Western blot analysis of mouse embryonic fibroblast (MEFs) cultured from homozygous mutant embryos confirmed the absence of Psme1 and Psme2 gene expression. (J:72533)