Fig. 1. Stress fiber formation induced by Fhos mutant proteins. (A) HeLa cells were transfected with vectors encoding the indicated mutant proteins of Fhos or RhoAG14V. Cells were fixed 16 hours after the addition of DNA-lipofectamine, and expressed proteins were detected by GFP fluorescence or immunostaining for the Myc epitope (left panel). F-actin was detected by phalloidin staining (right panel). Bar, 20 µm. (B) The structure of Fhos and its truncation mutants. Numbers denote amino acid positions in Fhos. Although the FH2 domain is originally defined as a conserved sequence of approximately 100 residues, the analysis of additional formins revealed that the similarity extends over about 500 amino acids (Frazier and Field, 1997; Zeller et al., 1999). The FH2 domain of Fhos (amino acids 613-1053) is also delineated by the extended definition. All constructs were tagged with GFP at the N-termini. The effect of each mutant on the induction of actin stress fibers is summarized on the right.