title: Caenorhabditis elegans UNC-45 is a component of muscle thick filaments and colocalizes with myosin heavy chain B, but not myosin heavy chain A.
abstract: In the nematode Caenorhabditis elegans, animals mutant in the gene encoding the protein product of the unc-45 gene (UNC-45) have disorganized muscle thick filaments in body wall muscles. Although UNC-45 contains tetratricopeptide repeats (TPR) as well as limited similarity to fungal proteins, no biochemical role has yet been found. UNC-45 reporters are expressed exclusively in muscle cells, and a functional reporter fusion is localized in the body wall muscles in a pattern identical to thick filament A-bands. UNC-45 colocalizes with myosin heavy chain (MHC) B in wild-type worms as well as in temperature-sensitive (ts) unc-45 mutants, but not in a mutant in which MHC B is absent. Surprisingly, UNC-45 localization is also not seen in MHC B mutants, in which the level of MHC A is increased, resulting in near-normal muscle thick filament structure. Thus, filament assembly can be independent of UNC-45. UNC-45 shows a localization pattern identical to and dependent on MHC B and a function that appears to be MHC B-dependent. We propose that UNC-45 is a peripheral component of muscle thick filaments due to its localization with MHC B. The role of UNC-45 in thick filament assembly seems restricted to a cofactor for assembly or stabilization of MHC B.
authors.affiliation: Department of Biological Sciences, University of Alberta, Edmonton, Alberta, T6G 2E9, Canada.
authors.forename: W
authors.initials: W
authors.lastname: Ao
authors.forename: D
authors.initials: D
authors.lastname: Pilgrim
mesh_terms: D000818:Animals; D017173:Caenorhabditis elegans; D029742:Caenorhabditis elegans Proteins; D005455:Fluorescent Antibody Technique; D017930:Genes, Reporter; D049452:Green Fluorescent Proteins; D015801:Helminth Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D008164:Luminescent Proteins; D008954:Models, Biological; D018832:Molecular Chaperones / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism; D009124:Muscle Proteins / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism; D009132:Muscles / Q000737:chemistry* / Q000648:ultrastructure; D018995:Myosin Heavy Chains / Q000302:isolation & purification* / Q000378:metabolism; D011485:Protein Binding; D020033:Protein Isoforms / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D011993:Recombinant Fusion Proteins; D020449:Repetitive Sequences, Amino Acid
chemical_list: D029742:Caenorhabditis elegans Proteins; D015801:Helminth Proteins; D008164:Luminescent Proteins; D018832:Molecular Chaperones; D009124:Muscle Proteins; D020033:Protein Isoforms; D011993:Recombinant Fusion Proteins; C107348:unc-45 protein, C elegans; D049452:Green Fluorescent Proteins; D018995:Myosin Heavy Chains