A loxP site flanked beta-geo (lacZ (beta-galactosidase) and neomycin resistance gene fusion) cassette was inserted into the intron upstream of exon P. A further loxP site was inserted into the intron downstream of exon P+2. These P exons encode ATP-binding P loops. Subsequent cre-mediated recombination created this null allele with the beta-geo cassette and exons P, P+1 and P+2 deleted. (J:239635)