IDENTIFICATION OF CDNA CLONES ENCODING TH E T-CELL RECEPTOR-BETA CHAIN IN THE RAINBOW-TROUT (ONCORHYNCHUS-MYKISS)

Using a two-step PCR strategy, we have cloned several cDNA segments en coding the T-cell receptor beta chain in a Teleost fish, the rainbow t rout (Oncorhynchus mykiss). The nine clones analyzed encode identical N-terminal V beta regions which present limited sequence similarities with several mammalian TcR V beta chains, from residue Tyr-35 to resid ue Ser-95. These V beta regions are followed by V beta-D beta-J beta-l ike regions which are different in all the sequenced clones, and by id entical C beta regions. The trout C beta domain (156 amino acids) is m ost related to the chicken and to amphibian (axolotl) C beta domains b ut no cysteine residue appears in the hinge region. Like in other vert ebrae C beta s, the TM region carries a positively charged lysine resi due (Lys-271). The intracytoplasmic domain is virtually absent. The po ssibility to analyze the structure, expression and diversity of a T-ce ll receptor chain in a Teleost fish model will be important for our fu ture understanding of the evolution of specific immune recognition in vertebrates.