Abstract

Actin Rearrangement-Inducing Factor of Baculoviruses Is Tyrosine Phosphorylated and Colocalizes to F-Actin at the Plasma Membrane Stephan Dreschers 1 , Renza Roncarati 2 , and Dagmar Knebel-Mörsdorf 1 , * Max Planck Institute for Neurological Research and Department of Neurology, University of Cologne, Cologne, Germany, 1 and Department of Medicine and Public Health, University of Verona, Verona, Italy 2 ABSTRACT In previous studies we have identified actin rearrangement-inducing factor 1 as an early gene product of Autographa californica multicapsid nuclear polyhedrosis virus that is involved in the remodeling of the actin cytoskeleton. We have constructed viral recombinants with a mutated Arif-1 open reading frame that confirm the causal link of Arif-1 expression and the actin rearrangement observed as accumulation of F-actin at the plasma membrane at 3 to 7 h postinfection. Infection with Arif mutant viruses leads to the loss of actin accumulation at the plasma membrane in TN-368 cells, although in the course of infection, early actin cables and nuclear F-actin are observed as in wild-type-infected cells. By immunofluorescence studies, we have demonstrated the localization of Arif-1 at the plasma membrane, and confocal imaging reveals the colocalization to F-actin. Accordingly, the ∼47-kDa Arif-1 protein is observed exclusively in membrane fractions prepared at 4 to 48 h postinfection, with a decrease at 24 h postinfection. Phosphatase treatment suggests that Arif-1 is modified by phosphorylation. Antibodies against phosphotyrosine precipitate Arif-1 from membrane fractions, indicating that Arif-1 becomes tyrosine phosphorylated during the early and late phases of infection. In summary, our results indicate that functional Arif-1 is tyrosine phosphorylated and is located at the plasma membrane as a component of the actin rearrangement-inducing complex.