Structural analysis of the CD3 zeta/eta locus of the rat. Expression of zeta but not eta transcripts by rat T cells.
We analyzed the structure and pattern of expression of rat TCR zeta- and eta-chains to investigate if these components function in activation and development of rat T cells. The rat zeta cDNA contained the complete open reading frame coding for a polypeptide of 164 amino acids and the 5' and 3' noncoding sequences. Comparison of the amino acid sequence to those of mouse and human counterparts revealed a high degree of similarity, more than 85% homology among all three species except for the signal peptide, which was especially high in the cytoplasmic domain including the nucleotide binding site and the possible tyrosine phosphorylation sites. Furthermore, we determined the nucleotide sequences of a rat genomic eta-like sequence located in the 3' region of the rat zeta-gene. Although it showed a high level of nucleotide similarity to mouse and human counterparts, 90.4 and 78.9%, respectively, the deduced polypeptide was very short (only 28 residues) and markedly divergent from the mouse and human eta-specific polypeptides due to frameshift mutations. Transcription of rat zeta was shown to be highly restricted to T cells; abundantly in thymocytes and scarcely in peripheral T cells. Surprisingly, the rat eta transcript could not be detected in any rat tissues so far tested by Northern blot analysis and even by the sensitive reverse transcription-polymerase chain reaction method, whereas it was readily detected in mouse thymus. These findings suggest that the zeta-chain has conserved roles in the TCR assembly and TCR-mediated signaling. However, the eta-chain seems not to be indispensable because of its structural diversity among these three species characterized to date and the apparent lack of eta expression in the rat.
Itoh
Y
Y
Department of Pathology, School of Medicine, Sapporo Medical University, Japan.
Matsuura
A
A
Kinebuchi
M
M
Honda
R
R
Takayama
S
S
Ichimiya
S
S
Kon
S
S
Kikuchi
K
K
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002874:Chromosome Mapping; D018076:DNA, Complementary / Q000302:isolation & purification; D005091:Exons; D006801:Humans; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics*; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D012333:RNA, Messenger / Q000032:analysis*; D051381:Rats; D011919:Rats, Inbred Strains; D011948:Receptors, Antigen, T-Cell / Q000737:chemistry / Q000235:genetics*; D012689:Sequence Homology, Nucleic Acid; D013601:T-Lymphocytes / Q000276:immunology / Q000378:metabolism*
D018076:DNA, Complementary; D008565:Membrane Proteins; D012333:RNA, Messenger; D011948:Receptors, Antigen, T-Cell; C054979:antigen T cell receptor, zeta chain