A time-resolved interaction analysis of Bem1 reconstructs the flow of Cdc42 during polar growth

Abstract

Cdc42 organizes cellular polarity and directs the formation of cellular structures in many organisms. By locating Cdc24, the source of active Cdc42, to the growing front of the yeast cell, the scaffold protein Bem1, is instrumental in shaping the cellular gradient of Cdc42. This gradient instructs bud formation, bud growth, or cytokinesis through the actions of a diverse set of effector proteins. To address how Bem1 participates in these transformations, we systematically tracked its protein interactions during one cell cycle to define the ensemble of Bem1 interaction states for each cell cycle stage. Mutants of Bem1 that interact with only a discrete subset of the interaction partners allowed to assign specific functions to different interaction states and identified the determinants for their cellular distributions. The analysis characterizes Bem1 as a cell cycle–specific shuttle that distributes active Cdc42 from its source to its effectors. It further suggests that Bem1 might convert the PAKs Cla4 and Ste20 into their active conformations.

The unconventional prefoldin RPB5 interactor mediates the gravitropic response by modulating cytoskeleton organization and auxin transport in Arabidopsis

“…Yeast Bud27 can interact with PFD2 and PFD6 (Ito et al, 2001; Deplazes et al, 2009; Wang et al, 2012). To investigate the potential interaction between AtURI and PFD members in Arabidopsis , we performed the split‐ubiquitin system assay (Johnsson and Varshavsky, 1994; Grinhagens et al, 2020) by fusing AtURI to the C‐terminal part of ubiquitin (Cub) and PFDs to the N‐terminal part of ubiquitin (Nub). The results showed that AtURI could interact with both PFD2 and PFD6, but not with PFD1, PFD3, PFD4, or PFD5 (Figure 4A).…”

“…Yeast cells producing two interacting proteins fused to the Nub and Cub fragments will grow on medium containing 5‐FOA. Yeast transformation and analysis were based on previous studies (Johnsson and Varshavsky, 1994; Grinhagens et al, 2020).…”

Type V myosin focuses the polarisome and shapes the tip of yeast cells

“…This activity might be less important during bud site assembly, in which formation of the polarity patch is more rigidly defined by landmark proteins ( Lai et al, 2018 ; Chiou et al, 2017 ). The when and where of polarisome nucleation might depend on physical links between PNCs and Cdc42 GTP and/or Bem1 ( Evangelista et al, 1997 ; Grinhagens et al, 2020 ).…”

Transient septin sumoylation steers a Fir1-Skt5 protein complex between the split septin ring

“…Fir1 is predicted to present multiple linear interaction motifs within a predominately unfolded structure (Fig. 1A) (Brace et al, 2019) (Grinhagens et al, 2020; Jumper et al, 2021). Fir1 binds to Smt3 through its SUMO-interacting motif (SIM) and was recently shown to localize to the bud neck during cell abscission (Hannich et al, 2005; Uzunova et al, 2007; Brace et al, 2019; Grinhagens et al, 2020).…”