The polyclonal rabbit antibody against p22 was a gift from Dr Susan C.Baker at Loyola University, IL. The chicken polyclonal antibody against hnRNP A1 was produced by Aves Labs, Inc. (Tigard, OR) by immunizing chickens with the puri®ed mouse hnRNP A1 protein expressed in bacteria. The polyclonal anti-Flag antibody was purchased from Af®nity Bioreagents (Golden, CO). The goat polyclonal antibody against actin was obtained from Santa Cruz Biotechnology (Santa Cruz, CA). The mouse monoclonal antibody against the N protein has been described previously (Fleming et al., 1983) .