(A) Exon 10 and its surroundings in the mouse CFTR gene. (B) The targeting construct CF Neo2. (C) The CFTR gene expected after targeting. (D) Details of the nucleotide and deduced amino acid sequences (numbered) predicted for the junction between the 5' part of exon 10 and MClNeo after targeting; italicized amino acids are not coded by the normal CFTR gene. Restriction sites important in construction of the targeting DNA or used for analysis of targeted colonies are shown. B, Bam HI; K, Kpn I; N, Nco I; O, Not I; S, Sst I; U, Stu I; X, Xmn I; Y, Sty I; sites in parentheses were destroyed during ligation. Sites and directions of primers 1-4 used for PCR analysis are indicated. Wavy lines show the amplified fragments that are characteristic of targeting. The sizes of some restriction enzyme fragments used for Southern analysis are indicated; vertically hatched box shoes the Bam HI/Sty I CFTR-related probe used for hybridization.