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© The Rockefeller University Press,
0021-9525/2000//375 $5.00
The Journal of Cell Biology, Volume 148, Number 2,
, 2000 375-384
Original Article |
Caenorhabditis elegans Unc-45 Is a Component of Muscle Thick Filaments and Colocalizes with Myosin Heavy Chain B, but Not Myosin Heavy Chain a
dave.pilgrim{at}ualberta.ca
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.
Key Words: tetracopeptide repeats • CRO1/SHE4 • unc-54 • myo-3 • myogenesis
© 2000 The Rockefeller University Press
Abbreviations used in this paper: GFP, green fluorescent protein; MHC, myosin heavy chain; TPR, tetratricopeptide repeats; (ts), temperature-sensitive; UNC-45, protein product of the unc-45 gene.
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