MYO1/YHR023W Summary Help

Standard Name MYO1
Systematic Name YHR023W
Feature Type ORF, Verified
Description Type II myosin heavy chain; required for wild-type cytokinesis and cell separation; localizes to the actomyosin ring; binds to myosin light chains Mlc1p and Mlc2p through its IQ1 and IQ2 motifs respectively (1, 2, 3, 4 and see Summary Paragraph)
Name Description MYOsin
Chromosomal Location
ChrVIII:151666 to 157452 | ORF Map | GBrowse
Gene Ontology Annotations All MYO1 GO evidence and references
  View Computational GO annotations for MYO1
Molecular Function
Manually curated
Biological Process
Manually curated
Cellular Component
Manually curated
Regulators 2 genes
Classical genetics
Large-scale survey
198 total interaction(s) for 135 unique genes/features.
Physical Interactions
  • Affinity Capture-MS: 31
  • Affinity Capture-RNA: 1
  • Affinity Capture-Western: 8
  • Co-purification: 1
  • FRET: 2
  • PCA: 3
  • Reconstituted Complex: 3
  • Two-hybrid: 62

Genetic Interactions
  • Dosage Rescue: 28
  • Phenotypic Enhancement: 3
  • Phenotypic Suppression: 5
  • Synthetic Growth Defect: 13
  • Synthetic Lethality: 27
  • Synthetic Rescue: 11

Expression Summary
Length (a.a.) 1,928
Molecular Weight (Da) 223,634
Isoelectric Point (pI) 6.35
Phosphorylation PhosphoGRID | PhosphoPep Database
sequence information
ChrVIII:151666 to 157452 | ORF Map | GBrowse
Last Update Coordinates: 2011-02-03 | Sequence: 1996-07-31
Subfeature details
Most Recent Updates
Coordinates Sequence
CDS 1..5787 151666..157452 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 | Entrez Gene | Entrez RefSeq Protein | MIPS | Search all NCBI (Entrez) | UniProtKB
Primary SGDIDS000001065

MYO1 encodes the only class II myosin heavy chain in budding yeast (2). As part of the actomyosin ring, Myo1p plays a critical role in cytokinesis (3). Early in the cell cycle, Myo1p localizes to a ring at the presumptive bud site and remains at the mother-bud neck until cytokinesis is completed (5, 1). Formation, but not maintenance, of the contractile ring requires the intact septin collar at the bud neck (The septins are encoded by CDC3, CDC10, CDC11, and CDC12) (5, 1, 6). Late in anaphase, F-actin (Act1p) and the IQGAP-related protein, Iqg1p, also accumulate in the neck ring (5). Incorporation of F-actin into the neck ring depends on Myo1p. At the end of anaphase the actinomyosin ring exhibits an F-actin-dependent decrease in size, presumably due to contraction (1).

There is controversy in the literature over whether MYO1 is an essential gene (5, 1). A myo1 mutant is inviable in W303, displaying a terminal phenotype of chains of large round cells, indicative of a cytokinesis defect (5). However, in other strains, myo1 mutants are viable and able to undergo a form of cell division (1). Genetic analysis suggests that at least one of these strains harbors an extragenic suppressor that may function to upregulate distinct pathways to partition the cytoplasm. For example, the suppressor may promote the insertion of membrane and/or septum formation at the division site (3). In fact, both of these processes are directly coupled to cytokinesis (7, 4, 8).

The catalytic domain of Myo1p is located in the N-terminus while the C-terminus contains a coiled-coiled domain interrupted by a hinge region (9). Remarkably, the non-catalytic tail domain can be recruited to the site of division and is sufficient for constriction and cytokinesis (10). Between the head and tail are two IQ domains. Class II myosins are regulated by two light chains, an essential light chain (ELC) and a regulatory light chain (RLC) that interact with the myosin through the IQ motifs (9). Mlc1p is the ELC for Myo1p and interacts with the IQ1 motif. However, binding of Mlc1p to Myo1p does not appear to play a major role in regulating Myo1p, but instead regulates actin ring formation and targeted secretion through interactions with Myo1p, Iqg1p, and Myo2p. Mlc2p is the RLC for Myo1p and interacts with the IQ2 motif. Mlc2p most likely plays a role in the disassembly of the Myo1p ring in vivo (4).

Class II myosins are found in many other organisms, and include both muscle myosins and nonmuscle myosins (11). Nonmuscle class II myosins have been implicated in cytokinesis in several organisms including Drosophila, C. elegans, and S. pombe (12). MYO1 is similar to human MYH11, a smooth muscle myosin heavy chain (OMIM). In some people, mutations in MYH11 give rise to a leukemia or familial aortic aneurysm.

Last updated: 2006-09-20 Contact SGD

References cited on this page View Complete Literature Guide for MYO1
1) Bi E, et al.  (1998) Involvement of an actomyosin contractile ring in Saccharomyces cerevisiae cytokinesis. J Cell Biol 142(5):1301-12
2) Brown SS  (1997) Myosins in yeast. Curr Opin Cell Biol 9(1):44-8
3) Tolliday N, et al.  (2003) Direct evidence for a critical role of myosin II in budding yeast cytokinesis and the evolvability of new cytokinetic mechanisms in the absence of myosin II. Mol Biol Cell 14(2):798-809
4) Luo J, et al.  (2004) Identification and functional analysis of the essential and regulatory light chains of the only type II myosin Myo1p in Saccharomyces cerevisiae. J Cell Biol 165(6):843-55
5) Lippincott J and Li R  (1998) Sequential assembly of myosin II, an IQGAP-like protein, and filamentous actin to a ring structure involved in budding yeast cytokinesis. J Cell Biol 140(2):355-66
6) Dobbelaere J and Barral Y  (2004) Spatial coordination of cytokinetic events by compartmentalization of the cell cortex. Science 305(5682):393-6
7) Schmidt M, et al.  (2002) In budding yeast, contraction of the actomyosin ring and formation of the primary septum at cytokinesis depend on each other. J Cell Sci 115(Pt 2):293-302
8) VerPlank L and Li R  (2005) Cell cycle-regulated trafficking of Chs2 controls actomyosin ring stability during cytokinesis. Mol Biol Cell 16(5):2529-43
9) May KM, et al.  (1998) Yeast myosin II: a new subclass of unconventional conventional myosins? Cell Motil Cytoskeleton 39(3):195-200
10) Lord M, et al.  (2005) Cytokinesis depends on the motor domains of myosin-II in fission yeast but not in budding yeast. Mol Biol Cell 16(11):5346-55
11) Cheney RE, et al.  (1993) Phylogenetic analysis of the myosin superfamily. Cell Motil Cytoskeleton 24(4):215-23
12) Glotzer M  (1997) The mechanism and control of cytokinesis. Curr Opin Cell Biol 9(6):815-23