The aim of the proposed research is to determine the gene structure of a major family of cell surface glycoproteins, collectively termed T200, which are present in different yet similar forms on the different lymphocyte lineages. Special emphasis will be directed toward determining how expression of the different forms of the molecules in this family is regulated. A genomic cloning strategy based on the ability of L cells to express T200 after transfection with DNA form lymphoid lines will be used to clone the T200 gene(s). The gene sequences encoding the different molecular forms will be compared with each other and the germline arrangement to determine whether gene rearrangement plays a role in the expression of these molecules. Using a genomic clone, the RNA and cDNA can be prepared for each of the different T200 forms and compared in order to detect any differences in RNA processing. The proposed research will also focus on molecular variations in T200 expression. Variations provided by evolution include the T200 genes of other species, including man, and the allelic forms of murine T200 genes. Additional variations have been selected in the laboratory and include structural gene mutants and revertants of these mutants. The goal of these studies will be to learn more about T200 expression and the function of the T200 glycoproteins. The gene clones will provide the means to investigate the change in T200 expression during differentiation in in vitro lymphocyte systems.