The association between the TCRalphabeta-CD3gammaepsilondeltaepsilon hexamers and zeta2 homodimers in the endoplasmic reticulum (ER) constitutes a key step in TCR assembly and export to the T cell surface. Incompletely assembled TCR-CD3 complexes are degraded in the ER or the lysosomes. A previously described Jurkat variant (J79) has a mutation at position 195 on the TCR Calpha domain causing a phenylalanine to valine exchange. This results in a lack of association between TCRalphabeta-CD3gammaepsilondeltaepsilon hexamers and zeta2 homodimers. Two main hypotheses could explain this phenomenon in J79 cells: TCR-CD3 hexamers may be incapable of interacting with zeta2 due to a structural change in the TCR Calpha region; alternatively, TCR-CD3 hexamers may be incapable of interacting with zeta2 due to factors unrelated to either molecular complex. In order to assess these two possibilities, the TCR-CD3 membrane-negative J79 cells were treated with ethylmethylsulfonate and clones positive for TCR membrane expression were isolated. The characterization of the J79r58 phenotypic revertant cell line is the subject of this study. The main question was to assess the reason for the TCR re-expression. The TCR on J79r58 cells appears qualitatively and functionally equivalent to wild-type TCR complexes. Nucleotide sequence analysis confirmed the presence of the original mutation in the TCR Calpha region but failed to detect compensatory mutations in alpha, beta, gamma, delta, epsilon or zeta chains. Thus, mutated J79-TCR-CD3 complexes can interact with zeta2 homodimers. Possible mechanisms for the unsuccessful TCR-CD3 interaction with zeta2 homodimers are presented and discussed.

T cell receptor (TCR)/CD3 complex assembly takes place in the endoplasmic reticulum (ER). Normal TCR/ CD3 complexes egress from the ER to the cis-Golgi, where the interaction with z 2 homodimers occurs. This interaction leads to further uncontrolled transport of TCR/CD3/z molecules to the cell surface. The purpose of the present experiments was to determine firstly the basis for the impact of the phe 195 / 216 . val mutations on TCR/CD3 expression in Jurkat cells, and secondly why mutated J79-cell TCRab/CD3 hexamers are prevented from interacting with z 2 homodimers. We found that phe . val mutations cause serious perturbations in a so far undefined hydrophobic area formed by the two phe 195/216 on b-strand F and aromatic/large hydrophobic amino acids on neighboring b-strands B and A in Ca and Cb domains, respectively. In addition, TCR/CD3 hexamers and z 2 homodimers colocalize in normal Jurkat T cells, in revertant J79r58 cells, and in J79 cells transfected with wild-type TCRa cDNA but not in J79 mutant cells (confocal microscopy). Furthermore, mutated TCR/CD3 complexes seem to be actively retained in the ER in J79 cells but not in revertant J79r58 cells by a nondominant mechanism. We propose that a hitherto undefined ER-retention molecule controls both the protein structure and egress of TCR/CD3 complexes from the ER of ab and gd T cells.

The Spatial Data Transfer Standard (SDTS) was designed to be capable of representing virtually any data model, rather than being a prescription for a single data model. It has fallen short of this ambitious goal for a number of reasons, which this paper investigates. In addition to issues that might have been anticipated in its design, a number of new issues have arisen since its initial development. These include the need to support explicit feature de® nitions, incremental update, value-added extensions, and change tracking within large, national databases. It is time to consider the next stage of evolution for SDTS. This paper suggests development of an Object Pro® le for SDTS that would integrate concepts for a dynamic schema structure, OpenGIS interface, and CORBA IDL.

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