Abstract
Srv2/CAP is a highly conserved actin binding protein. Extensive previous analysis has shown that yeast Srv2/CAP increases cellular actin dynamics by both stimulating cofilin-mediated severing of actin filaments (an activity mediated by its N-terminus) and by catalyzing the conversion of actin monomers from an ADP- to ATP- bound state (an activity mediated by its C-terminus). On the other hand, the regulatory activities of mammalian CAP have remained largely uncharacterized. We show here that the activities of mouse CAP1 are indistinguishable from those of yeast Srv2. First, in biochemical assays CAP1 strongly enhanced actin filament disassembly by cofilin, and stimulated nucleotide exchange (ADP for ATP) on actin monomers. Second, these activities depended on specific sequences in CAP1 that are shared with Srv2 and found to mediate the same activities in Srv2. Third, expression of CAP1 could fully rescue srv2∆ defects in yeast cell growth and actin organization. These observations demonstrate that both the biochemical and cellular activities of Srv2 in regulating actin dynamics are highly conserved from yeast of mammals