Differential expression and distinct structure of 69- and 100-kDa forms of 2-5A synthetase in human cells treated with interferon.

Using specific monoclonal and polyclonal antibodies, the induction, synthesis and subcellular localization of 69- and 100-kDa forms of 2',5'-oligoadenylate (2-5A) synthetase (p69 and p100) were investigated in alpha-interferon-treated human HeLa and Daudi cells. Although both p69 and p100 were induced by interferon, there were significant differences in the interferon dose-response and the kinetics of synthesis of each protein in these cell lines. Both proteins are localized mainly in the cytoplasm. However, immunoenzymatic staining analysis of interferon-treated cells indicated that a proportion of p69 is concentrated around the nuclei and the rest is distributed in a specific pattern in the cytoplasm whereas p100 is found in a diffuse state in the cytoplasm. In accord with its association to cell membranes, p69 is myristilated. The [35S]cysteine and [3H]myristate-labeled p69 preparations were resolved by two-dimensional gel isoelectric focusing with pI values in the pH range of 7.0-8.0 and 7.0-7.5, respectively. These observations suggested the existence of two forms of p69 which might be complexed together as a dimer. In favor with a dimeric form of p69, in gel filtration experiments the peak of p69 was routinely found in fractions corresponding to a molecular mass of 160 kDa whereas p100 was recovered as a monomer. Taken together, these results indicate that p69 and p100 have distinct characteristics and that their expression is a specific property of each cell type in response to interferon.