Figure 2.

Positions of residues mutated in arp2 alleles and Arp2 expression levels in the mutant strains. (A) The residues mutated in each arp2 allele (Table 1) are highlighted on the crystal structure of rabbit skeletal muscle actin (1ATN). The crystal structure of Arp2 is not shown because only half of its structure is solved (Robinson et al. 2001). The four subdomains (I, II, III, and IV) are indicated, and the Arp2-specific loop in subdomain III was inserted from a crystallized portion of Arp2 (1K8K). The specific residues mutated in each allele are shown in space-fill and color-coded: arp2-1 (red), arp2-2 (yellow), arp2-3 (orange), arp2-4 (cyan), arp2-5 (purple), arp2-6 (green), and arp2-7 (blue). (B) Arp2 protein levels were compared in wild-type and arp2 mutant cells grown to log phase by immunoblotting total cell extracts with Arp2 antibodies. The same samples were immunoblotted with tubulin antibodies as a loading control. Although some lanes on the tubulin blot show a lower signal (e.g., arp2-7), repeated experiments demonstrated that variation was due to inefficient transfer of some lanes and that tubulin and Arp2 levels are similar in whole-cell extracts from these strains (not shown).