Actin rearrangement-inducing factor of baculoviruses is tyrosine phosphorylated and colocalizes to F-actin at the plasma membrane

In previous studies we have identified actin rearrangement-inducing factor 1 as an early gene product of Autographa californica multicapsid nuclear po lyhedrosis virus that is involved in the remodeling of the actin cytoskelet on. We have constructed viral recombinants with a mutated Arif-1 open readi ng frame that confirm the causal link of Arif-1 expression and the actin re arrangement 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 observe d as in wild-type-infected cells. By immunofluorescence studies, we have de monstrated the localization of Arif-1 at the plasma membrane, and confocal imaging reveals the colocalization to F-actin. Accordingly, the similar to 47-kDa Arif-1 protein is observed exclusively in membrane fractions prepare d at 4 to 48 h postinfection, with a decrease at 24 h postinfection. Phosph atase treatment suggests that Arif-1 is modified by phosphorylation, Antibo dies against phosphotyrosine precipitate Arif-1 from membrane fractions, in dicating that Arif-1 becomes tyrosine phosphorylated during the early and l ate phases of infection. In summary, our results indicate that functional A rif-1 is tyrosine phosphorylated and is located at the plasma membrane as a component of the actin rearrangement-inducing complex.