Figure 7.

The functional surfaces of the Arp1p filament. (A) Homotypic contact regions in the Arp1p filament. A single Arp1p monomer (green) makes contacts with four surrounding monomers. The charge clusters belonging to the polypeptide chain of the central monomer that make contact with surrounding monomers are shown in yellow. The side chains of charge clusters from the four adjacent monomers that contact the central monomer are shown in four shades of blue (only the relevant side chains are shown, the rest of the polypeptide is not shown for clarity). Opposite faces of the central monomer are shown. The schematic magenta box represents the monomer's inner facing surface; the teal box represents the outer face. (B) The Arp1p filament pseudo-wild-type surface. ARP1 and ACT1 alleles are mapped onto a section of their respective filaments. The “pointed-end” is up and the “barbed-end” is down in all images. Although likely shorter than the actual Arp1p filament, a pentamer is shown to allow visualization of trends, while still providing sufficient detail. Red indicates Ts^– and lethal alleles; yellow indicates pseudo-wild type. (C) The positive-charge and mass-action rescue surfaces of Arp1p. We compared the electrostatic potential of Act1p and Arp1p pentamers. Arp1 has a net positive charge surface that encompasses the bulk of Ts^– and lethal alleles. Red, –3.5; blue, 3.5 (bottom, left and middle filaments). For mass-action rescue, red, rescued, and blue, nonrescued (bottom, right filament). Note the coincident position of the positive-charge surface and the nonrescued alleles. For clarity, pseudo-wild-type alleles are not shown; they would be found along the three projections to the right. The red circle indicates the Arp1-specific projection encompassing arp-38, 100, and 115. A schematic representation of the Arp1p filament consisting of five boxes, each with a magenta inner face and teal outer face, serves as an orienting guide to the relative position of monomers in each filament.