Characterisation of the Hs6st1 gene trap allele. (A) Schematic representation of the Hs6st1-gene trapped locus. Hs6st1 consists of two exons separated by a 35-kb intron. The gene trap vector has inserted into intron1 and abolishes wild-type Hs6st1 transcripts. (B) Southern blot analysis on BamHI/ClaI digested genomic DNA from wild-type, Hs6st1+/− and Hs6st1−/− tissue using radiolabelled DNA probes 1–5. Probe 3 hybridised to a 7-kb restriction fragment in wild-type and a 4-kb restriction fragment in Hs6st1 mutants, indicating that the gene trap vector had inserted into the 7-kb BamHI–ClaI restriction fragment in the Hs6st1 allele. (C) Probe 3 hybridised to a 3.9-kb BamHI/EcoRV restriction fragment in wild-type and a 6.6-kb fragment in Hs6st1 mutants. (D) PCR primers P1/P2 amplify a 205-bp region of Hs6st1 intron1 at the gene trap insertion site. This PCR product was absent in Hs6st1−/− mutants, but present in wild-type and Hs6st1+/− heterozygotes. Primers hP1 and hP2 amplify a 316-bp region within the hPLAP coding sequence, which is present in Hs6st1+/− and Hs6st1−/− mutants, but absent in wild-types.