FIG. 1.

Structure and modification of the proximal serpin subcluster. At top is the proximal serpin subcluster, showing the locations of the human α1AT, ATR, and CBG genes, with exons indicated by black bars. Arrows indicate the positions of 21 DHSs that are present on wild-type human chromosome 14 in Fao-1 rat hepatoma hybrids; 18 of these sites are expression associated (gray arrows) and 4 are constitutive (black arrows). The bottom portion shows excision of an 8.0-kb DNA segment upstream of the 315-bp α1AT hepatic promoter in DT40 hybrids. (A) The locus is targeted with the recombination substrate containing two ∼4-kb arms of homology, a hisD selection cassette flanked by loxP sites (flags), and a DipA counterselection cassette. (B) Homologous recombinants are identified by Southern hybridization using a diagnostic BglII band shift from the wild-type 3.0-kb DNA fragment to the mutant fragment of 7.7 kb. (C) The hisD selection cassette is removed by transient transfection with Cre recombinase. Cre recombinants were identified by a diagnostic 4.5-kb BglII fragment after Southern hybridization.