Isolation and Characterization of the Porcine Tissue Kallikrein Gene Family S.C. Fernando, R.D. Geisert, B.A. Roe and U. DeSilva Story in Brief Kallikreins are members of a multigene family of serine proteases that are widespread throughout living organisms. They are found in diverse tissue specific patterns and are known to have highly diverse physiological functions. To gain insight into the structure and evolutionary origin of the kallikrein gene region in the pig, we isolated several BAC clones containing members of the porcine tissue kallikrein gene family and have characterized the porcine kallikreins. Sequence analysis of the greater kallikrein region has revealed the presence of 13 kallikrein genes in the porcine genome, among which 11 are novel porcine kallikrein genes. Furthermore, in an effort to understand the tissue specific expression profile of the porcine kallikrein genes family members, we have analyzed the expression pattern of the kallikrein genes across a wide array of porcine tissue. Key Words: Kallikrein, Gene Expression, Serine Proteases, Porcine, Pig Introduction During the last three decades, extensive research on tissue kallikrein gene families of humans and rodents have been carried out (Evans et al., 1987). These studies have helped us better understand the structural and functional similarities among tissue kallikreins. Kallikreins are members of a multigene family of serine proteases that are widespread throughout living organisms (Gan et al., 2000). They show high degree of substrate specificity and demonstrate highly diverse physiological functions (Evans et al., 1987). Kallikreins show high degree of conservation at both gene and protein structure level, and co-localize or organize into the same chromosomal locus in all species they are studied in (Evans et al., 1987; Yousef and Diamandis, 2001; Yousef et. al. 2003). Based on the conservation of the primary and tertiary structures and the enzymatic activities among kallikreins, it is hypothesized that all known serine proteases arose from a common ancestor through gene and/or chromosomal duplication during the course of evolution, which may have caused the kallikrein gene family to be clustered in the genome (Gan et al., 2000; Yousef and Diamandis, 2001). Comparison of the kallikrein family members among species reveal that there is a greater level of conservation within species than among orthologous genes across species, suggesting that recombination has occurred within a species leading to concerted evolution (Wines, 1991). Currently 15 kallikrein genes with diverse expression profiles have been identified in humans. All co- localize to the same locus on chromosome 19q13.3 – q13.4 (Riegman et al., 1992; Yousef and Diamandis, 2001). Several are implicated in breast, ovarian and other human cancers (Yousef and Diamandis, 2001).The mouse kallikrein gene family is the largest family of kallikreins known to date and consists of 24 members, among which, 14 code for active proteins while the remaining are pseudogenes (Evans et al., 1987; Yousef et al., 2003).