Molecular cloning of a carp Jak3 from activated leukocytes

Janus kinases (Jaks) are involved in a signalling pathway leading to tyrosi ne phosphorylation, which is the key step in transducing cytokine signals f rom the external environment to the nucleus. We report here the molecular c loning of carp Jak3. A partial cDNA of the Jak homologue was initially iden tified from a cDNA pool obtained by subtracting the cDNAs from Con A-induce d carp head kidney leukocytes with those from uninduced carp head kidney le ukocytes. The entire coding sequence was assembled by sequencing both stran ds of cDNA clones amplified by using anchored PCR reaction. The complete cD NA was cloned by specific primers designed against the partial cDNAs and th en sequenced to assure accuracy of the complete sequence. Sequence analysis reveals an ORF encoding a protein of 1026 amino acids, with the unique pre sence of two carboxy-terminal kinase and pseudokinase domains. The cDNA clo ne shows approximate to 52-50%, 50-48.2%, 42-39% and 35-39% amino acid iden tity with the known Jak3s, Jak2s, Jak1s and Tyk2s, respectively. The sequen ce of the amino acid residues within the N-terminal JH domains of the carp Jak homologue shows higher similarities with the regions of human Jak3 than with human Jak2. The carp Jak is expressed as a single 4.5 Kb transcript a t low levels in the head kidney and the spleen, with the RNA level increasi ng when leukocytes are activated with con A. The trace transcript was also detected by RT-PCR in the carp liver, muscle and skin, but not in the egg s ample. Sequence analysis and pattern of expression suggest that this cDNA r epresents the carp Jak3 (accession number in GenBank: AF148993). (C) 2000 E lsevier Science B.V. All rights reserved.