Figure 9.

Model of Sla2p regulation and interactions. Sla2p exists in the cytoplasm and associated with cortical actin patches. Localization to the cortex is probably necessary for activity. Based on the N-terminal deletion and C-terminal truncation analysis of Sla2p, both termini of the protein contain a cortical actin patch localization signal. The unknown proteins that mediate Sla2p’s cortical patch localization are denoted X and Y. The C terminus has been demonstrated to contain an actin-binding site, so Y might be actin. The large, central coiled-coil domain potentially interacts with other proteins (Z). Indeed, Rvs167p has been reported to bind this domain of Sla2p in two-hybrid studies (Wesp et al., 1997). Rvs167 binds to Abp1p, which itself binds to Srv2p and to actin. When expressed alone, however, the coiled-coil domain is cytoplasmic, and thus this link seems to be insufficient for Sla2p localization. Regulation of the distribution and function of Sla2p could potentially be accomplished through interaction with any of a number of proteins. We have shown, however, that the actin-binding site located in the C-terminal talin-like domain is likely to be inactivated through a self-association with the upstream small coiled-coil domain of the protein. This interaction may also be sufficient to block the N-terminal and coiled-coil domain binding sites for proteins X and Z, as shown ii, or additional switches and signals may be involved, as depicted in i.