title: A mutation in the converter subdomain of Aspergillus nidulans MyoB blocks constriction of the actomyosin ring in cytokinesis.
abstract: We have identified a mutant allele of the Aspergillus nidulans homologue of myosin II (myoB; AN4706), which prevents normal septum formation. This is the first reported myosin II mutation in a filamentous fungus. Strains expressing the myoB(G843D) allele produce mainly aberrant septa at 30 °C and are completely aseptate at temperatures above 37 °C. Conidium formation is greatly reduced at 30 °C and progressively impaired with increasing temperature. Sequencing of the myoB(G843D) allele identified a point mutation predicted to result in a glycine-to-aspartate amino acid substitution at residue 843 in the myosin II converter domain. This residue is conserved in all fungal, plant, and animal myosin sequences that we have examined. The mutation does not prevent localization of the myoB(G843D) gene product to contractile rings, but it does block ring constriction. MyoB(G843D) rings at sites of abortive septation disassemble after an extended period and dissipate into the cytoplasm. During contractile ring formation, both wild type and mutant MyoB::GFP colocalize with actin--an association that begins at the pre-ring "string" stage. Down-regulation of wild-type myoB expression under control of the alcA promoter blocks septation but does not prevent actin from aggregating at putative septation sites--the actin rings, however, do not fully coalesce. Both septation and targeting of MyoB are blocked by disruption of filamentous actin using latrunculin B. We propose a model in which myosin assembly at septation sites depends upon the presence of F-actin, but assembly of the actin component of contractile rings depends upon normal levels of myosin only for the final stages of ring compaction.
authors: Department of Biology, Rhodes College, Memphis, TN 38112, USA. Electronic address: hill@rhodes.edu.
authors: Terry W
authors: TW
authors: Hill
authors: Department of Chemistry, Rhodes College, Memphis, TN 38112, USA.
authors: Loretta
authors: L
authors: Jackson-Hayes
authors: Department of Biology, Rhodes College, Memphis, TN 38112, USA.
authors: Xiao
authors: X
authors: Wang
authors: Department of Biology, Rhodes College, Memphis, TN 38112, USA.
authors: Brianna L
authors: BL
authors: Hoge
mesh_terms: D000199:Actins / Q000378:metabolism; D000205:Actomyosin / Q000502:physiology*; D000595:Amino Acid Sequence; D001233:Aspergillus nidulans / Q000235:genetics* / Q000502:physiology*; D048749:Cytokinesis / Q000502:physiology*; D025301:Hyphae / Q000648:ultrastructure; D024462:Myosin Type II / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D017354:Point Mutation; D017434:Protein Structure, Tertiary
chemical_list: D000199:Actins; D000205:Actomyosin; D024462:Myosin Type II
keywords: Contractile ring; Converter subdomain; Cytokinesis; Myosin II