Expression of FLAG-tagged p27 in sympathetic neurons grown in the presence of NGF and infected by an engineered Sindbis virus. A, B, Immunofluorescence staining with an antibody directed against the FLAG epitope of neurons in culture infected with Sindbis virus expressing p27-FLAG (A) or containing the p27 control sequence (B). Arrows indicate the locations of individual neurons. Neurons were stained 2 d after infection.