MOLECULAR-CLONING OF RAT JAK3, A NOVEL MEMBER OF THE JAK FAMILY OF PROTEIN-TYROSINE KINASES

We have cloned and sequenced a cDNA (JAK3) encoding a novel member of the JAK family of protein tyrosine kinases. JAK3 was identified by RT- PCR of rat mesangial cells using degenerate oligonucleotide primers, a nd a full-length clone was isolated from a rat spleen cDNA library. Th e primary structure of JAK3 showed cDNA with an open reading frame of 1,100 amino acids which comprises th PTK catalytic domain and a second kinase-related domain characteristic for JAK kinase. JAK3 was phyloge netically shown to be most closely related to JAK2 among the previousl y known JAK family members, JAK1, JAK2 and Tyk2. Southern analysis rev ealed that JAK3 is a single copy gene and well conserved in the verteb ral genome. Northern analysis indicated that the 4.0 kb mRNA was trans cribed in a variety of tissues including spleen, lung, kidney and inte stine.