InterPro2GO mapping assigns Cdc42 generic small-GTPase molecular functions (GTP binding, GTPase activity) and small GTPase-mediated signal transduction based on Rho-family domain signatures. These are correct generic functions for Cdc42.

EC-to-GO mapping assigned 'G protein activity' (GO:0003925) via EC 3.6.5.2. This is appropriate: GO:0003925 is the general molecular-switch function (GTP/GDP cycling + effector binding) whose narrow synonyms include "small monomeric GTPase activity", and EC 3.6.5.2 (small monomeric GTPase) maps to it. It correctly applies to the Rho-family GTPase Cdc42 and overlaps with the GTPase activity (GO:0003924) annotation.

Phylogenetic (PANTHER) inference assigns conserved Cdc42/Rho functions: actin filament organization, establishment of cell polarity, endocytosis, and protein kinase (PAK) binding, all of which are independently supported by direct fission yeast experiments.

Maps UniProt subcellular location (cell membrane, lipid anchor) to plasma membrane; consistent with prenylation-dependent membrane localization.

ARBA machine-learning annotations recapitulate experimentally supported localizations (cell tip, site of polarized growth, plasma membrane) and establishment of cell polarity.

Functional GFP-Cdc42p localizes to the medial cell-division site during cytokinesis and to the cell periphery and internal membranes; medial localization depends on the actin cytoskeleton and the actomyosin ring.

Gef1p is a Cdc42-specific GEF that binds inactive Cdc42p and stimulates its guanine nucleotide exchange in vitro; gef1 and scd1 share an essential Cdc42-activating function.

Cdc42p is essential for proliferation and rod-shaped morphology; the two GEFs Gef1p and Scd1p form a ring at the division site that recruits active Cdc42p to the septation site during cytokinesis.

Hob3p (BAR-domain protein) interacts directly with Cdc42p and is required to recruit and concentrate Cdc42p at the cell division site for cytokinesis.

GTP-bound active Cdc42 (CRIB-GFP) is concentrated at growing cell ends with F-actin, where the GAP Rga4 is excluded; bipolar Cdc42 activation requires Pom1-dependent Rga4 localization. GTP-Cdc42 binds CRIB-domain effectors including PAKs and WASp.

This study characterizes Rga2 as a GAP for Rho2 (not Cdc42); it does not directly assay Cdc42 intrinsic GTPase activity.

Orb6 NDR kinase spatially restricts Cdc42 (and Cdc42-dependent For3 and GEF Gef1) to cell tips; loss of Orb6 activity causes lateral cortex localization of Cdc42 and increased cell diameter.

In invasive filaments, activated Cdc42 (with Spo20, Bgs4, Crn1) becomes concentrated at the single growing cell tip.

The GAP Rga4 (cell sides) and GEF Scd1 (cell tips) establish a gradient of activated Cdc42 at the tip plasma membrane that determines growth-zone size and normal cell width. Small GTPases are switches with intrinsic GTP hydrolysis facilitated by GAPs.

A cdc42L160S thermosensitive allele has actin-independent membrane traffic defects: decreased acid phosphatase secretion, vesicle accumulation, vacuole fragmentation, and exocyst mislocalization, indicating Cdc42 regulates polarized secretion and vesicle fusion.

Cdc42 is required for exocyst function and for correct transport/recycling of the glucan synthases Bgs1 and Bgs4 to the plasma membrane at cell tips.

Under low-level pheromone signaling, active Cdc42 with GEF Scd1 and scaffold Scd2 form dynamic colocalizing zones (cortical polarity patches) that sample the cell periphery to orient growth toward a mating partner at the mating projection tip.

Thermal stress transiently decreases Cdc42 activity and induces monopolar growth; under these conditions Cdc42 activity at the lateral/growing cortex is altered.

During mating, Ras1-GTP hydrolysis is required to coordinate active Cdc42 into a single growth zone; hyperactive Ras1 causes disorganized Cdc42 and actin and elongation from multiple tips, supporting Cdc42's role in mating projection assembly.

A functional internally tagged Cdc42 (mCherry/sfGFP sandwich) is enriched at cell tips and division sites, present along cell sides and on internal (nuclear, vacuolar) membranes, and is trafficked on exocytic vesicles (accumulates sub-apically upon Sec8 depletion). CAAX-mediated membrane targeting is essential; Cdc42-GTP shows slower membrane mobility, consistent with positive-feedback accumulation at sites of activity.

Cdc42 localizes to the cell division site/cleavage furrow and is activated with distinct spatiotemporal pattern in cytokinesis - Gef1-dependent before ring constriction (promoting timely constriction) and Scd1-dependent after (promoting septum formation).

Active Cdc42 localizes to the cell cortex and the mitotic actomyosin ring; the two GEFs Scd1 (local, membrane-associated) and Gef1 (global, cytosolic) are coordinated via microtubules and the Tea1-Tea4-Pom1/Rga4 axis.

A Cdc42 feedforward pathway in which active Cdc42 recruits the scaffold Scd2 (and thereby Scd1) underlies GEF interplay during polarity and cytokinesis, illustrating Cdc42's role as a signaling hub/adaptor coordinating its own activators.

Active Cdc42 at the division site prevents early (precocious) Rho1 activation during cytokinesis through its effector kinase Pak1, coordinating timely septum formation.

Cdc42 functions in cell-cell fusion (cytogamy) during sexual reproduction, concentrating at the mating projection tip/fusion site; mating and fusion require higher Cdc42 protein levels than mitotic polarized growth.

The PAK kinase Shk1 (Pak1) physically and functionally interacts with Cdc42, forming a Ras/Cdc42 signaling module required for normal morphology and mating.

Scd1, Scd2, Cdc42, and GTP-bound Ras1 act cooperatively to form a protein complex; Scd2 binds both Scd1 and Cdc42. This pathway is required for mating and cell morphology (establishment of polarity / mating projection).

cdc42+ is essential; null cells arrest as small, round, dense cells, and GTP-binding-domain mutants give large misshapen cells, establishing Cdc42 as a controller of polarized cell growth. The protein partitions between soluble and particulate (membrane) pools.

Rho1, not Cdc42, directly activates (1-3)beta-D-glucan synthase; neither cdc42+ nor constitutively active cdc42 (V12G, Q61L) alleles affect glucan synthase activity when overexpressed. Thus Cdc42's link to beta-glucan biosynthesis is indirect at best.

Shk1 (Pak1), Cdc42, and Skb1 form a ternary complex in vivo, with Skb1 binding an Shk1 region distinct from the Cdc42-binding site.

Shk2 (Pak2) is a PAK that binds Cdc42 in vivo and in vitro and participates with Cdc42 in Ras-dependent morphological control and mating-response pathways.

Pak2p is a p21-activated kinase whose membrane localization and biological activity depend in part on its interaction with Cdc42p, consistent with Cdc42 functioning as an activator of PAK kinases.