(A). Mouse PAF-AH genomic locus and targeting strategy. E: EcoRI site; P, loxP site; S, SalI site; X: XhoI site. (B). Long-range PCR analysis used to detect correct targeting in ES cell clones. Each clone was evaluated using control PCR primers (p1 and p2) and diagnostic primers (p1 and p3). The bottom panel shows examples of positive (1c8) and negative (1c9, 1c10) ES clones. (C). Germline transmission of the targeted allele to the F1 generation was determined by PCR using a variety of primer combinations. The right panels show analyses of wild-type (−) and targeted (+) ES cell DNA, tail DNA from a chimeric mouse (χ), and DNA from F1+/+ and F1−/+ mice. (D). Levels of serum PAF-AH activity in wild-type (n=20) and PAF-AH deficient mice (n=14).