Biochemical characterization of the murine activated lymphocyte alloantigen Ly-6E.1 controlled by the Ly-6 locus.

The Ly-6.1 alloantigen defined by monoclonal antibody SK70.94 and expressed predominantly on activated lymphocytes has been immunoprecipitated from lysates of cells biosynthetically radiolabeled with 35S-methionine. On SDS-polyacrylamide gel electrophoresis the reduced antigen appeared as a doublet of 17 and 18 kD. The nonreduced polypeptides had higher mobilities indicating intrachain but not interchain disulfide linkages. The nonreduced form was detectable by immunoperoxidase stain on blots after SDS-PAGE. This showed both polypeptide species contained the antigenic epitope. Labeling in the presence of tunicamycin did not change the apparent m.w. suggesting the absence of N-linked carbohydrate. Pulse-chase data are inconsistent with a strict precursor-product relationship between the two polypeptides and give a half-life for the antigen in 2-day Con A blast cells of about 4 1/2 hr. A highly purified preparation of this antigen displayed a similar electrophoretic pattern and, in the presence of deoxycholate, eluted from a Sephacryl S-200 gel filtration column with a partition coefficient equivalent to that of a 31-kD soluble globular protein. Because of the associated detergent and probable deviation from globularity, this is an over-estimate of the size of the native molecule, and is more consistent with the native molecule being a single polypeptide chain rather than a dimer. Isoelectric focusing of this material showed microheterogeneity with at least five bands between pI 4 and 5. Another monoclonal antibody, HD-42, which had been isolated on the basis of its specificity for a fibrosarcoma antigen subsequently found to be Ly-6 related, precipitated the same polypeptides. Furthermore, no obvious difference was evident between precipitates from Con A-activated lymphocytes and Meth A fibrosarcoma cells.