Purification of two components of mouse L cell interferon: electrophoretic demonstration of interferon proteins

Mouse L cell interferon induced by Newcastle disease virus was purified by the procedure described previously (Yamamoto et al. 1974) followed by gel filtration. The two fractions obtained containing interferon species S (36000 daltons) and F (24000 daltons), respectively, were analysed electrophoretically at pH 4-3, or in the presence of sodium dodecyl sulphate (SDS) at pH 7-2. In both fractions, interferon activity was invariably associated with distinct protein bands. In the F-containing fraction there were essentially no other proteins, and in the S-containing fraction, impurity proteins were well separated from the interferon activity. The apparent mol. wt. determined by SDS-gel electrophoresis showed little or no dependence on gel concentration, suggesting that the interferons had low carbohydrate contents, and did not change after reduction with thiol reagents in SDS and urea.