EXPRESSION, CHARACTERIZATION, AND GENOMIC STRUCTURE OF CARP JAK1 KINASE GENE

A 3.7-kb cDNA encodes the carp JAK1 kinase of 1,156 amino acid residue s, The overall amino acid sequence identity between carp JAK1 and muri ne JAK1, JAK2, JAK3, and human TYK2 is 57%, 35.5%, 31.3%, and 42.4%, r espectively. In addition, carp JAK1 shows higher sequence homology to mammalian JAK1 in both the kinase-like (JH2) and kinase (JH1) domains (approximately 70% identity). Therefore, carp JAK1 is a homolog of mam malian JAK1. To investigate the possible function of JH2 domain, full- length, and various truncated forms of carp JAK1 were produced in the baculovirus system, Our results demonstrate that c-JH1 and c-JH2 assoc iate with each other and c-JH2 can be tyrosine-phosphorylated by c-JAK 1 and by c-JH(1 + 2), The JAK1 gene was also isolated from a carp geno mic library and characterized, This gene is divided into 24 exons span ning at least 31 kb of genomic DNA. Exon 1 contains the 5'-untranslate d region and exon 2 contains the putative translation initiation site. The 2,5-kb DNA region upstream of the transcription initiation site c ontains numerous potential binding sites for transcription factors inc luding NF-IL6, HNF-5, AP1, GHF-5, and E2A. When this DNA fragment was placed upstream of the chloramphenicol acetyltransferase (CAT) reporte r gene and transfected into a carp CF cell line, it could drive the sy nthesis of CAT enzyme 16 times more efficiently than the promoterless pCAT-Basic. Deletion analysis defined a positive regulatory region bet ween -1,023 and -528. A smaller region (-181 to + 59) without any typi cal TATA-box sequences, G + C-rich sequences, or other binding sequenc es for known transcription factors still had promoter activity, Constr ucts without this region did not have detectable promoter activity, Th is suggests that this region of DNA may play an important role in the expression of carp JAK1 gene.