YFR016C Antibody

What is YFR016C/Aip5 and what is its primary function in yeast cells?

YFR016C, also known as Aip5, functions as part of an actin nucleation complex in Saccharomyces cerevisiae. It has been identified as a novel subunit of a complex that regulates the number of actin filaments at sites of polar growth . This protein interacts with Bud6 (an actin nucleation-promoting factor) and Spa2 (a polarisome scaffold protein), contributing to the formation of actin cables below the tip of yeast cells . Aip5 represents an important component of the polarisome, which comprises a network of proteins that organizes polar growth in yeast and filamentous fungi .

Methodological approach: To study Aip5's basic function, researchers typically employ gene deletion studies combined with actin visualization techniques to observe the resulting phenotype. Fluorescence microscopy using phalloidin staining can reveal changes in actin cable distribution and abundance when Aip5 is absent.

What cellular phenotypes are observed in YFR016C deletion mutants?

Methodological approach: When analyzing Δyfr016c phenotypes, researchers should employ quantitative image analysis of actin structures using standardized staining protocols and imaging parameters to accurately measure differences in actin cable numbers compared to wild-type cells.

What are the functional domains of YFR016C/Aip5 and their binding partners?

Aip5 has distinct functional domains that mediate its interactions with other proteins:

• N-terminal region: Binds to the polarisome scaffold protein Spa2

• C-terminal region: Binds to the actin nucleation-promoting factor Bud6

Both of these interactions are required for proper localization of Aip5 at bud tip and neck, and are necessary to stimulate the formation of actin cables . The protein shows approximately 22% similarity over a segment of 108 amino acids to Uso1p, a protein involved in ER-vesicle transport .

Methodological approach: Domain mapping through truncation mutants and site-directed mutagenesis can identify critical residues for protein-protein interactions. Yeast two-hybrid or split-ubiquitin assays with Aip5 fragments can verify domain-specific binding partners.

How does YFR016C/Aip5 contribute to polarisome assembly and actin nucleation mechanisms?

Aip5 functions within the polarisome complex to promote actin cable formation at sites of polarized growth. The current model suggests that Aip5 acts as a molecular bridge that helps position or activate the actin nucleation machinery . By binding simultaneously to Spa2 (via its N-terminal region) and Bud6 (via its C-terminal region), Aip5 helps integrate these components into a functional complex .

The precise mechanism appears to involve a synergistic interaction where Spa2 provides localization signals for the complex, while Bud6 works with the formin Bni1 to nucleate actin filaments . Aip5 enhances this process, potentially by optimizing the spatial arrangement or activation state of these factors. This is supported by the observation that cells lacking Aip5 show reduced actin cable formation despite the presence of other nucleation factors .

Methodological approach: In vitro reconstitution assays using purified components can directly measure Aip5's effect on actin nucleation rates. Live-cell imaging with fluorescently tagged components can track the temporal assembly of polarisome factors and how Aip5 influences this process.

What is the relationship between YFR016C/Aip5 and myosin motor proteins in cell polarity?

Aip5 has been identified as an interaction partner of both Myo1p (type II myosin involved in cytokinesis) and Myo2p (type V myosin essential for polarized secretion) . This association with myosin motors suggests Aip5 may play a role in coordinating actin organization with motor-driven processes.

Significantly, localization of Spa2GFP to sites of polarized growth depends on functional Myo2p but not on Myo1p . Additionally, Aip5, like Myo2p, co-sediments with F-actin in an ATP-sensitive manner, suggesting a potential association with actin via direct or indirect interaction with Myo2p .

These findings indicate that Aip5 may be involved in mediating polarized localization of polarity proteins via Myo2p-dependent transport along actin cables .

Methodological approach: Co-immunoprecipitation experiments combined with actin co-sedimentation assays in the presence/absence of ATP can elucidate the nature of Aip5's interaction with myosin motors and actin. Conditional mutants of myosin proteins can reveal dependency relationships.

How do environmental conditions or stress responses affect YFR016C/Aip5 function?

While the search results don't directly address this question, this represents an important research direction. Given Aip5's role in actin organization and cell polarity, its function may be modulated during stress responses that affect the cytoskeleton.

Methodological approach: Researchers could examine Aip5 localization, abundance, and protein modification status under various stress conditions (osmotic shock, temperature shifts, nutrient limitation). Phosphoproteomics analysis could identify regulatory modifications that occur in response to specific stresses. Genetic interactions between Aip5 and stress-response pathways could be assessed through synthetic genetic array analysis.

What techniques are recommended for studying YFR016C/Aip5 protein-protein interactions?

Several complementary approaches are effective for studying Aip5 interactions:

• Co-immunoprecipitation (Co-IP):

  • Use epitope-tagged Aip5 (HA-tag is mentioned in the search results)

  • Perform reciprocal Co-IPs with tagged interaction partners

  • Analyze by western blot or mass spectrometry to identify interacting proteins

• Yeast Two-Hybrid and Split-Ubiquitin Assays:

  • The search results specifically mention split-ubiquitin as a technique used for studying Aip5

  • This system employs CRU (C-terminal ubiquitin) and Nub (N-terminal ubiquitin) fusion constructs

  • Expression of Aip5 fragments fused to either half of ubiquitin can map specific interaction domains

• Subcellular Fractionation:

  • Differential centrifugation as described in the search results can separate cellular components

  • Compare fractionation patterns of Aip5 with known interactors

  • The search results describe a method using increasing centrifugation speeds (2,000g, 30,000g, 100,000g) to create S1/P1, S2/P2, and S3/P3 fractions

Methodological approach: When designing interaction studies, researchers should consider both in vivo techniques like split-ubiquitin and co-IP as well as in vitro binding assays with purified components to distinguish direct from indirect interactions.

What are optimal methods for visualizing YFR016C/Aip5 localization in yeast cells?

For effective visualization of YFR016C/Aip5:

• Genomically Integrated GFP Fusions:

  • The search results describe construction of genomically integrated Aip5-GFP fusions using pRS304 vector

  • Integration at the endogenous locus ensures native expression levels

  • Verification by PCR using diagnostic primers is recommended

• Live-Cell Imaging Considerations:

  • Use appropriate exposure settings to minimize photobleaching

  • Consider time-lapse imaging to track dynamic changes during the cell cycle

  • Co-visualization with markers for polarisome components (Spa2, Bud6) can provide context

• Controls and Validation:

  • Confirm functionality of the fusion protein by testing for complementation of Δyfr016c phenotypes

  • Include proper controls (untagged strains, cells with known localization patterns)

  • Use quantitative methods to assess co-localization with interaction partners

Methodological approach: Time-lapse microscopy combined with quantitative image analysis can provide insights into the dynamics of Aip5 localization during cell cycle progression or in response to perturbations.

How can researchers generate and verify YFR016C mutants for functional studies?

The search results describe several effective approaches:

• CRISPR/Cas9 System:

  • Guide-RNA construction into a CRISPR/Cas9 plasmid as described in the Wyrick Lab protocol

  • This approach was used to create specific deletions, such as removing residues 1000-1131 in YFR016c

  • Verification by PCR using appropriate diagnostic primers

• Homologous Recombination:

  • Replace the YFR016C ORF with an antibiotic resistance cassette as described in the search results

  • Linearize integration plasmids using unique restriction sites within the genomic sequence (e.g., AflII or BglII sites mentioned)

  • Verify integration by PCR with diagnostic primers

• Construction of Domain Mutants:

  • PCR amplification of specific fragments from genomic DNA with appropriate primers containing restriction sites

  • Expression under native or regulated promoters (e.g., PMET17 promoter mentioned)

  • Shuttle vectors like pRS313 can be used for expression of mutant constructs

Methodological approach: When creating mutants, researchers should design experiments to test both localization and function. Complementation tests with wild-type constructs should be performed to confirm that phenotypes are due to the specific mutation rather than secondary effects.

How does YFR016C/Aip5 interact with the actin cytoskeleton?

YFR016C/Aip5 interacts with the actin cytoskeleton in several key ways:

• Actin Cable Formation: Aip5 stimulates the formation of actin cables. Cells lacking Aip5 display a reduced number of actin cables, indicating its positive role in actin filament generation .

• Co-sedimentation with F-actin: Aip5, like Myo2p, co-sediments with F-actin in an ATP-sensitive manner . This suggests that Aip5 associates with actin, either directly or indirectly through proteins like Myo2p.

• Polarisome Complex: Aip5 is part of the polarisome, which includes the formin Bni1 and the actin nucleation-promoting factor Bud6 . Together, these proteins catalyze the formation of actin cables below the tip of yeast cells.

• Localization at Growth Sites: Aip5 localizes to sites of polarized growth (bud tip and neck), where actin assembly is actively occurring . This positioning allows it to contribute to site-specific actin organization.

Methodological approach: Actin co-sedimentation assays with purified components can determine whether Aip5 binds directly to actin or requires intermediary proteins. Pyrene-actin assembly assays can quantify the effect of Aip5 on actin polymerization rates in vitro.

What is the relationship between YFR016C/Aip5 and cell separation or cytokinesis?

While the search results don't extensively address Aip5's direct role in cytokinesis, they provide some relevant insights:

• Interaction with Cytokinesis Factors: Aip5 interacts with Myo1p , which is a type II myosin involved in cytokinesis. This suggests a potential role for Aip5 in this process.

• Localization Pattern: Aip5 localizes to both the bud tip and neck , with the latter being the site of cytokinesis in yeast cells.

• Genetic Interactions: The search results mention "an enhanced cell-separation defect in a myo1spa2 strain at 37°C" , suggesting that polarisome components like Spa2 (which interacts with Aip5) contribute to cytokinesis alongside Myo1p.

Methodological approach: Time-lapse imaging of Aip5-GFP during cytokinesis, particularly in strains with compromised cytokinesis machinery, could reveal dynamic behaviors relevant to the cell separation process. Genetic interaction studies between Aip5 and known cytokinesis factors could identify functional relationships.

How do the molecular interactions of YFR016C/Aip5 contribute to its cellular functions?

Aip5's cellular functions are mediated through specific molecular interactions:

• Spa2 Binding (N-terminal region):

  • Provides proper localization to growth sites

  • Integrates Aip5 into the polarisome complex

  • May help position Aip5 relative to other polarity factors

• Bud6 Binding (C-terminal region):

  • Connects Aip5 to the actin nucleation machinery

  • Contributes to stimulation of actin cable formation

  • May enhance Bud6's nucleation-promoting activity

• Myosin Interactions:

  • Association with Myo1p and Myo2p suggests roles in motor-dependent processes

  • May link the polarisome to myosin-based transport or force generation

  • Could facilitate coordination between actin assembly and motor activity

These interactions collectively position Aip5 as a multifunctional adapter protein within the polarisome, helping to coordinate actin assembly with spatial cues at sites of polarized growth.

Methodological approach: Structure-function studies using domain swaps or chimeric proteins could delineate how specific interactions contribute to distinct aspects of Aip5 function. Reconstitution of minimal systems in vitro could test whether these interactions are sufficient for particular activities.