Physical mapping of the rat tissue kallikrein family in two gene clusters by analysis of P1 bacteriophage clones

In several mammalian species the tissue kallikreins constitute gene families whose members encode a highly related subgroup of the simple serine proteases. Previous characterization of kallikrein genes in the rat identified 13 of the potential 15-20 members present in this species. To characterize comprehensively all members of the rat gene family and to define the linkage of family members, we have isolated clones bearing kallikrein genes from a rat genomic library constructed with the P1 bacteriophage vector pAd10-SacBII. Library pools containing kallikrein genes were identified by polymerase chain reaction with primers complementary to regions highly conserved among members of the rat gene family. Individual members of the family within the library pools were identified with gene-specific PCR assays that rely upon short divergent regions among the family members. Detection of multiple kallikrein family members within single library pools suggested tight linkage of the individual genes. Isolation and analysis of 12 kallikrein P1 clones confirmed the linkage of gene family members and established a physical map for two clusters of genes at the kallikrein locus. The linkage relationships of the known gene family members within the two gene contigs are rKLK1-rKLK3-rKLK7-rKLK9 and rKLK8-rKLK2-rKLK6-rKLK4-rKL10-rKLK12. Pulsed-field electrophoretic analysis of rat genomic DNA demonstrated linkage between the two gene clusters, which form an extended locus that is most narrowly defined by a 440-kb BssHII fragment, and identified an unmethylated CpG island that is tightly linked to this locus.