Ci. Park et al., Cloning of Japanese flounder Paralichthys olivaceus CD3 cDNA anal gene, and analysis of its expression, IMMUNOGENET, 53(2), 2001, pp. 130-135
Two distinct CD3 homologue cDNAs, CD3-1 and CD3-2, were isolated from a Jap
anese flounder leukocyte cDNA library. CD3-1 consisted of 961 bp encoding 1
78 amino acid residues, and CD3-2 consisted of 927 bp encoding 182 amino ac
id residues. The two deduced amino acid sequences had an identity of 95.1%,
and neither had N-linked glycosylation sites. The identities between the J
apanese flounder CD3s and previously reported CD3s (CD3 epsilon, CD3 gamma,
or CD3 delta) of Xenopus laevis, chicken, and various mammals were approxi
mately 25%. The Japanese flounder CD3s had an extracellular domain, a CXXCX
E motif, and an immunoreceptor tyrosine-based activation motif (ITAM), each
of which are important characteristics of CD3 chains. Furthermore, the pos
itions of four cysteine residues in the extracellular domain were preserved
in both of the Japanese flounder CD3s. A phylogenetic tree based on the am
ino acid sequences confirmed that the Japanese flounder CD3s are closer to
CD3 epsilon than to CD3 gamma and CD3 delta. However, the gene structure of
Japanese flounder CD3 is identical to the chicken and Xenopus CD3 gamma/de
lta genes and the mammalian CD3 delta gene. Southern blot hybridization and
the DNA sequence of the CD3 gene of homocloned Japanese flounder indicated
that the CD3 gene exists as a single copy. Southern blot hybridization als
o showed the presence of a polymorphic variant of Japanese flounder CD3. An
RT-PCR analysis detected Japanese flounder CD3 mRNA in several organs that
contained lymphocytes. The proportion of CDS-positive cells in the periphe
ral blood leukocytes was 34.9%.