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-,
-,
-, and
-Chains1
Department of Aquatic Biosciences, Tokyo University of Fisheries, Minato, Tokyo, Japan
We have isolated and identified all four TCR
,
,
, and
cDNAs and genomic clones from a Japanese flounder leukocyte cDNA library and bacterial artificial chromosomal genomic library. Numerous TCR transcripts were sequenced to examine the variability against antigenic peptide, and were shown hypervariability on their complementarity-determining region 3 (CDR3) loops. Among CDR3s, CDR3
showed a long and broad length distribution, indicating greater similarity to that of Ig. From cDNA sequences and genomic gene analysis of each chain, we found that flounder TCR
,
, and
have two different C gene segments, while the TCR
C region exists as a single segment. The flounder C
s and C
s showed different lengths in the connecting peptide (CP) region between the different types of polypeptides. The C
1 gene consists of two exons, one that encodes an extracellular Ig-like domain (exon 1) and the other that encodes either a very short or possibly a lacking CP region, a transmembrane region, and a cytoplasmic tail (exon 2); these are located within TCR
gene locus. Southern blot analysis, using the bacterial artificial chromosomal genomic DNA clones, revealed that the C
2 gene segment, which has a long CP region and different genomic organization to the C
1 gene, exists on same gene locus as the TCR
-chain. This suggests that the flounder possesses very unique genomic DNA organization and gene loci for TCR, C
/C
1, and C
/C
2.
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