Partition of E1A proteins between soluble and structural fractions of adenovirus-infected and -transformed cells

The partition of E1A proteins between soluble and structural framework fractions of human cells infected or transformed by subgroup C adenoviruses was investigated by using gentle cell fractionation conditions. A polyclonal antibody raised against a trpE-E1A fusion protein (K.R. Spindler, D.S.E. Rosser, and A. J. Berk, J. Virol. 132-141, 1984) synthesized in Escherichia coli was used to measure the steady-state levels of E1A proteins recovered in the various fractions by immunoblotting. The relative concentration of E1A proteins recovered in the soluble fraction of adenovirus type 2-infected cells was at least fivefold greater than the relative concentration in the corresponding fraction of transformed 293 cells. The observed distribution of E1A proteins was not altered by the sulfhydryl-blocking reagent N-ethylmaleimide. E1A proteins were recovered in nuclear matrix, chromatin, and cytoskeleton fractions after further fractionation of the structural framework fraction. However, the E1A protein species that could be identified by one-dimensional gel electrophoresis were not uniformly distributed among the subcellular fractions examined. The results obtained when fractionation was performed in the presence of the oxidation catalysts Cu2+ or (ortho-phenanthroline)2 Cu2+ indicate that E1A proteins can be efficiently cross-linked, via disulfide bonds, to the structural framework of both adenovirus-infected and adenovirus-transformed cells.