(A) Patch lifetimes ± standard deviation of Sla1-GFP at 25°C (white) or 37°C (gray) for ARP2 (SL5770), arp2-7 (SL5775), arp2-1 (SL5792), and arp2-2 (SL5780), respectively. * indicates p ≤ 0.0001 compared with ARP2 at comparable temperature, ^† indicates p ≤ 0.0003 compared with ARP2 at comparable temperature, ^# indicates p ≤ 0.0001 compared to same strain at 25 °C. (B) Patch lifetimes ± standard deviation of Abp1-RFP at 25°C (white) or 37°C (gray) for ARP2, arp2-7, arp2-1, and arp2-2, respectively. * Indicates p ≤ 0.0001 compared with ARP2, ^‡ indicates p ≤ 0.002 compared with ARP2 at comparable temperature, ^# indicates p ≤ 0.0001 compared to same strain at 25 °C. (C) Kymographs of Sla1-GFP and Abp1-RFP at either 25°C (upper) or 37°C (lower) illustrate the lifetimes and overlap of these factors over 240 sec. Time lapse movies were acquired with 2 sec intervals between frames, and using 250 msec exposures for both Sla1-GFP and Abp1-RFP.

(A) Schematic of S. cerevisiae genomic inserts contained in library plasmids pJD11, pJD12, pJD7 and pJD9, which were isolated as high copy suppressors of arp2-7 temperature sensitive growth. (B) ARP2 (BGY134), arp2-1 (BGY136), and arp2-7 (BGY142) strains transformed with empty vector (pBG006) or pGAL1-SYP1 (pBG287) were 10-fold serially diluted, plated on selective galactose-containing medium, and grown at 25 and 37°C. (C) Previously identified high copy suppressors of pfy1Δ [34] were transformed into the arp2-7 (BGY142) strain (BGY142). Transformants were 10-fold serially diluted, plated on selective medium, and grown at 25°C and 37°C. (D) ARP2, arp2-1 and arp2-7 strains containing SYP1 or syp1Δ were 5-fold serially diluted and grown at 30°C, 35.5°C or 37°C for 48 hours. (E) Schematic of Syp1 demonstrating regions of homology to F-BAR (Green) or AP μ (Brown) domains. Also highlighted are serine (Blue) and proline (Yellow) rich regions, possible Ark/Prk phosphorylation sites (T576, T588) and an NPF motif (Orange).

(A) Syp1-GFP localization in JDY175. A Z-stack of 0.25 uM sections (600 msec exposures) was deconvolved and projected onto a single plane. (B) Patch lifetimes ± standard deviation of indicated endocytic factors were obtained from 4 min time lapse movies taken at 600 msec exposures, 2 sec between frames. Data are from SL5863 (Ede1-Cherry), SL5806 (Syp1-GFP and Abp1-RFP), SL5862 (End3-Cherry). (C) Localization of Syp1-GFP combined with Ede1-Cherry (SL5863), End3-Cherry (SL5862), or Abp1-RFP (SL5806) in a single cross-section plane. Exposures were 1 sec for GFP and Cherry fusions; 800 msec for Abp1-RFP. Note yellow in the merge shows nearly complete overlap of Ede1 and Syp1, with only occasional overlap for Syp1-GFP and End3-Cherry (arrowheads). There is essentially no overlap between Syp1-GFP and Abp1-RFP. (D) Kymographs from time lapse movies of Syp1-GFP combined with Ede1-Cherry (SL5863), End3-Cherry (SL5862), or Abp1-RFP (SL5806). Exposures were 1 sec for GFP and Cherry fusions; 800 msec for Abp1-RFP, with 3 sec between frames. Note the nearly complete overlap of Syp1-GFP and Ede1-Cherry, whereas End3-Cherry appears near the end of the fluorescent lifetime of Syp1. Syp1-GFP disappears just prior to Abp1-RFP appearance. (E) Tile views showing timing of appearance and disappearance of Syp1-GFP with End3-Cherry (SL5862) or Syp1-GFP with Abp1-RFP (SL5806). Exposures are as indicated in panel D. Beginning frames showing the early phase of Syp1 have been trimmed. Tile views were aligned based on the known timing of End3 and Abp1 [10] The black arrow in the lower tile view indicates the transition point at which Syp1 disappears but Abp1 has not yet appeared.

(A) Sla1-GFP lifetimes (± standard deviation) in ARP2 (SL5770) or arp2-7 (SL5775) ± SYP1 2μ shifted to 37°C. * indicates p ≤ 0.0001 comparing ± SYP1 over-expression. (B) ABP1-RFP lifetimes (± standard deviation) shifted to 37°C in the same strains as above. (C) Kymographs of Sla1-GFP and Abp1-RFP at 37°C from strains indicated above. Time lapse movies were taken with 2 sec intervals between frames, and using 250 msec exposures for both Sla1-GFP and Abp1-RFP.

(A) Coomassie stained gel of full-length 6His-Syp1 purified from E. coli. (B) 3 μM actin (5% pyrene-labeled) was polymerized in the presence of 15 nM yeast Arp2/3 complex, 15 nM yeast Las17/WASp, and a range of concentrations of 6His-Syp1. (C) Concentration-dependent effects of 6His-Syp1 on rate of actin assembly induced by 15nM Las17/WASp and 15nM Arp2/3 complex. (D) 2 μM yeast or rabbit muscle actin (5% pyrene labeled) was assembled alone and in the presence of 10nM Arp2/3 complex and 10 nM Las17/WASp with and without 2.5 μM Syp1. (E) Quantification of data in panel D. Rates of actin assembly for reactions containing yeast actin and rabbit muscle actin and lacking Syp1 were both normalized to 1 for comparative purposes. (F) Schematic of Syp1 fragments that were purified and tested for inhibition of Las17/WASp-Arp2/3 complex activity. Each Syp1 fragment (>1 μM) was tested for effects on 15nM Las17/WASp and 15nM Arp2/3 complex. (G) Concentration-dependent effects of Syp1 (aa 265-565) on rate of actin assembly induced by 15nM Las17/WASp and 15nM Arp2/3 complex.

(A) 4 μM actin (5% pyrene-labeled) was polymerized in the presence of 10 nM yeast Arp2/3 complex and 10 nM yeast Las17/WASp or 20 nM yeast Arp2/3 complex and 200 nM yeast GST-VCA in the presence or absence of 2.5 μM Syp1. (B) Quantification of data from A. Rates of actin assembly for reactions containing Las17/WASp and GST-VCA domain but lacking Syp1 were normalized to 1 for comparative purposes. (C) Control beads or beads coated with Las17/WASp were incubated with soluble Syp1, then pelleted, and the supernatants were analyzed by SDS PAGE and Coomassie staining. (D) Quantification of data in C; levels of Syp1 in the supernatants were measured by densitometry.