STT4/YLR305C Summary Help

Standard Name STT4 1
Systematic Name YLR305C
Feature Type ORF, Verified
Description Phosphatidylinositol-4-kinase; functions in the Pkc1p protein kinase pathway; required for normal vacuole morphology, cell wall integrity, and actin cytoskeleton organization (2, 3, 4 and see Summary Paragraph)
Name Description STaurosporine and Temperature sensitive 5
Chromosomal Location
ChrXII:743863 to 738161 | ORF Map | GBrowse
Note: this feature is encoded on the Crick strand.
Gene Ontology Annotations All STT4 GO evidence and references
  View Computational GO annotations for STT4
Molecular Function
Manually curated
Biological Process
Manually curated
Cellular Component
Manually curated
Regulators 1 genes
Classical genetics
Large-scale survey
reduction of function
76 total interaction(s) for 52 unique genes/features.
Physical Interactions
  • Affinity Capture-MS: 15
  • Affinity Capture-Western: 4
  • Co-localization: 1
  • Reconstituted Complex: 1
  • Two-hybrid: 3

Genetic Interactions
  • Dosage Rescue: 7
  • Negative Genetic: 5
  • Phenotypic Enhancement: 2
  • Phenotypic Suppression: 3
  • Positive Genetic: 2
  • Synthetic Growth Defect: 2
  • Synthetic Lethality: 27
  • Synthetic Rescue: 4

Expression Summary
Length (a.a.) 1,900
Molecular Weight (Da) 214,605
Isoelectric Point (pI) 7.44
Phosphorylation PhosphoGRID | PhosphoPep Database
sequence information
ChrXII:743863 to 738161 | ORF Map | GBrowse
Note: this feature is encoded on the Crick strand.
Last Update Coordinates: 2011-02-03 | Sequence: 1996-07-31
Subfeature details
Most Recent Updates
Coordinates Sequence
CDS 1..5703 743863..738161 2011-02-03 1996-07-31
Retrieve sequences
Analyze Sequence
S288C only
S288C vs. other species
S288C vs. other strains
External Links All Associated Seq | E.C. | Entrez Gene | Entrez RefSeq Protein | MIPS | Search all NCBI (Entrez) | UniProtKB
Primary SGDIDS000004296

Phosphatidylinositol 4-kinases (ATP:phosphatidylinositol-4-phosphotransferase, EC are evolutionarily conserved enzymes that catalyze the formation of phosphatidylinositol 4-phosphate and ADP from phosphatidylinositol (PtdIns or PI) and ATP, the first step in the synthesis of phosphatidylinositol phosphates (6, 7). Two types of PtdIns 4-kinases (types II and III) have been identified based on their biochemical properties (6). Type III PtdIns 4-kinases all contain a common catalytic kinase domain, which is also found in type I PtdIns 3-kinases (8, 9). There are two type III PtdIns 4-kinases in S. cerevisiae, encoded by PIK1 and STT4 (10, 1). LSB6 encodes the single type II PtdIns 4-kinase in yeast (6, 7).

Pik1p is a soluble 125-kDa enzyme (11), and Stt4p is a plasma membrane-associated 215-kDa enzyme (1, 4). Together, Pik1p and Stt4p account for the vast majority of PtdIns 4-kinase activity in wild-type yeast cells (3). The two different type III PtdIns 4-kinases synthesize discrete pools of PtdIns 4-phosphate with essential roles in cell physiology (3). Overproduction of one of these type III PtdIns 4-kinases cannot compensate for a gene disruption in the other (3). Stt4p is homologous to mammalian PtdIns 4-kinase alpha, and Pik1p to mammalian PtdIns 4-kinase beta (8).

Stt4p is required for the maintenance of vacuole morphology, cell wall integrity, and actin cytoskeleton organization, as well as sphingolipid biosynthesis (3, 12). Stt4p also plays a role in the regulation of the intracellular transport of the aminophospholipid phosphatidylserine from the ER to the Golgi (13). Stt4p binds to the plasma membrane via the protein Sfk1p, where it promotes cell-wall synthesis, actin cytoskeleton organization, and the Rho1/Pkc1-mediated mitogen-activated protein kinase cascade (1, 3, 4, 7).

STT4 is an essential gene in some backgrounds, but not in others (14, 13). Conditional stt4 mutants are temperature-sensitive and can be rescued by sorbitol (1). stt4 deletion mutants lack most of the PtdIns 4-kinase activity that is detected in the wild-type, and arrest in the G2/M phase of the cell cycle (1, 2). Inactivation of Stt4p results in mislocalization of the Rho-GTPase guanine nucleotide exchange factor Rom2p (4), and also in the rapid attenuation of translation initiation (15). Synthetic genetic array (SGA) analysis using a temperature-sensitive allele of STT4 indicates that stt4(ts) cells can not tolerate perturbations in long chain fatty acid elongation (12).

About Phosphatidylinositol Phosphate Biosynthesis

The phosphorylated products of phosphatidylinositol (PtdIns, PI), collectively referred to as phosphoinositides or phosphatidylinositol phosphates (PtdInsPs, PIPs), are membrane-bound lipids that function as structural components of membranes, as well as regulators of many cellular processes in eukaryotes, including vesicle-mediated membrane trafficking, cell wall integrity, and actin cytoskeleton organization (reviewed in 16 and 17). PtdInsPs are also precursors of the water-soluble inositol phosphates (IPs), an important class of intracellular signaling molecules (reviewed in 18, 19 and 20).

The inositol ring of the membrane phospholipids and the water-soluble IPs are readily phosphorylated and dephosphorylated at a number of positions making them well suited as key regulators. PtdIns can be phosphorylated at one or a combination of positions (3', 4', or 5') on the inositol headgroup, generating a set of unique stereoisomers that have specific biological functions (reviewed in 16). These stereoisomers have been shown to be restricted to certain membranes (reviewed in 16). Phosphatidylinositol 4-phosphate (PtdIns4P) is the major PtdInsP species of the Golgi apparatus, where it plays a role in the vesicular trafficking of secretory proteins from the Golgi to the plasma membrane (reviewed in 16). Phosphatidylinositol 4,5-bisphosphate (PtdIns[4,5]P2) is the major species found at the plasma membrane and is involved in the regulation of actin cytoskeleton organization, as well as cell wall integrity, and heat shock response pathways (reviewed in 16). Phosphatidylinositol 3-phosphate (PtdIns3P) is found predominantly at endosomal membranes and in multivesicular bodies (MVB), where it plays a role in endosomal and vacuolar membrane trafficking. Phosphatidylinositol 3,5-bisphosphate (PtdIns[3,5]P2) is found on vacuolar membranes where it plays an important role in the MVB sorting pathway (reviewed in 16).

Phosphorylation and dephosphorylation of the inositol headgroups of PtdInsPs at specific membrane locations signals the recruitment of certain proteins essential for vesicular transport (17, and reviewed in 16). PtdInsPs recruit proteins that contain PtdInsP-specific binding domains, such as the well-studied pleckstrin homology (PH) domain that recognizes the phosphorylation pattern of specific PtdInsP inositol headgroups (reviewed in 16).

A number of kinases and phosphatases are involved in the generation and interconversions of PtdInsPs, the majority of which have been well conserved during evolution (reviewed in 16). The PtdInsP kinases, in contrast to the lipid phosphatases, have a higher degree of specificity. While each kinase appears to phosphorylate only one substrate, many of the lipid phosphatases can dephosphorylate a number of substrates.

Last updated: 2008-05-08 Contact SGD

References cited on this page View Complete Literature Guide for STT4
1) Yoshida S, et al.  (1994) A novel gene, STT4, encodes a phosphatidylinositol 4-kinase in the PKC1 protein kinase pathway of Saccharomyces cerevisiae. J Biol Chem 269(2):1166-72
2) Pramanik A, et al.  (1997) Cloning, characterization and identification of the gene encoding phosphatidylinositol 4-kinase. Cell Mol Biol (Noisy-le-grand) 43(7):1007-18
3) Audhya A, et al.  (2000) Distinct roles for the yeast phosphatidylinositol 4-kinases, Stt4p and Pik1p, in secretion, cell growth, and organelle membrane dynamics. Mol Biol Cell 11(8):2673-89
4) Audhya A and Emr SD  (2002) Stt4 PI 4-kinase localizes to the plasma membrane and functions in the Pkc1-mediated MAP kinase cascade. Dev Cell 2(5):593-605
5) Yoshida S, et al.  (1992) Characterization of a staurosporine- and temperature-sensitive mutant, stt1, of Saccharomyces cerevisiae: STT1 is allelic to PKC1. Mol Gen Genet 231(3):337-44
6) Han GS, et al.  (2002) The Saccharomyces cerevisiae LSB6 gene encodes phosphatidylinositol 4-kinase activity. J Biol Chem 277(49):47709-18
7) Shelton SN, et al.  (2003) Saccharomyces cerevisiae contains a Type II phosphoinositide 4-kinase. Biochem J 371(Pt 2):533-40
8) Fruman DA, et al.  (1998) Phosphoinositide kinases. Annu Rev Biochem 67():481-507
9) Odorizzi G, et al.  (2000) Phosphoinositide signaling and the regulation of membrane trafficking in yeast. Trends Biochem Sci 25(5):229-35
10) Flanagan CA, et al.  (1993) Phosphatidylinositol 4-kinase: gene structure and requirement for yeast cell viability. Science 262(5138):1444-8
11) Flanagan CA and Thorner J  (1992) Purification and characterization of a soluble phosphatidylinositol 4-kinase from the yeast Saccharomyces cerevisiae. J Biol Chem 267(33):24117-25
12) Tabuchi M, et al.  (2006) The phosphatidylinositol 4,5-biphosphate and TORC2 binding proteins Slm1 and Slm2 function in sphingolipid regulation. Mol Cell Biol 26(15):5861-75
13) Trotter PJ, et al.  (1998) A genetic screen for aminophospholipid transport mutants identifies the phosphatidylinositol 4-kinase, STT4p, as an essential component in phosphatidylserine metabolism. J Biol Chem 273(21):13189-96
14) Cutler NS, et al.  (1997) STT4 is an essential phosphatidylinositol 4-kinase that is a target of wortmannin in Saccharomyces cerevisiae. J Biol Chem 272(44):27671-7
15) Cameroni E, et al.  (2006) Phosphatidylinositol 4-Phosphate Is Required for Translation Initiation in Saccharomyces cerevisiae. J Biol Chem 281(50):38139-49
16) Strahl T and Thorner J  (2007) Synthesis and function of membrane phosphoinositides in budding yeast, Saccharomyces cerevisiae. Biochim Biophys Acta 1771(3):353-404
17) De Camilli P, et al.  (1996) Phosphoinositides as regulators in membrane traffic. Science 271(5255):1533-9
18) York JD  (2006) Regulation of nuclear processes by inositol polyphosphates. Biochim Biophys Acta 1761(5-6):552-9
19) Bennett M, et al.  (2006) Inositol pyrophosphates: metabolism and signaling. Cell Mol Life Sci 63(5):552-64
20) Bhandari R, et al.  (2007) Inositol pyrophosphate pyrotechnics. Cell Metab 5(5):321-3