Invariant proteins associated with guinea-pig Ia antigens

Abstract

Analysis of guinea-pig Ia immunoprecipitates by two-dimensional gel electrophoresis demonstrated the specific association of Ia molecules with several types of invariant proteins. These include a 33,000 mol. wt basic protein homologous to murine invariant chain (I i), and a set of 34,000–36,000 mol. wt proteins more acidic than I i (acidic invariant chain). Two 23,000–25,000 mol. wt nonpolymorphic proteins with pls of 6.0 and 6.5 were also observed in association with Ia, as was a basic protein of mol. wt 42,000. Pulse/chase studies using [ 35S]methionine demonstrated that I i, but not acidic invariant chain, was associated with newly synthesized Ia molecules. The amount of 35S-I i decreased greatly throughout the chase period. 35S-acidic invariant chain was clearly present in Ia precipitates by 30 min after Ia synthesis, but was not detected 4hr after synthesis. Only acidic invariant chain was associated with mature Ia antigens bound by the lectin Ricinus communis I. Our results indicate that guinea-pig invariant proteins are differentially bound by Ia molecules during maturation of Ia α- and β-chains, and suggest that acidic invariant chain could be a processed form of I i.