Abstract:
In Caenorhabditis elegans two M-line proteins, UNC-98 and UNC-96, are involved in myofibril assembly and/or mainte-
nance, especially myosin thick filaments. We found that CSN-5, a component of the COP9 signalosome complex, binds
to UNC-98 and -96 using the yeast two-hybrid method. These interactions were confirmed by biochemical methods. The
CSN-5 protein contains a Mov34 domain. Although one other COP9 signalosome component, CSN-6, also has a Mov34
domain, CSN-6 did not interact with UNC-98 or -96. Anti-CSN-5 antibody colocalized with paramyosin at A-bands in wild
type and colocalized with abnormal accumulations of paramyosin found in unc-98, -96, and -15 (encodes paramyosin)
mutants. Double knockdown of csn-5 and -6 could slightly suppress the unc-96 mutant phenotype. In the double
knockdown of csn-5 and -6, the levels of UNC-98 protein were increased and the levels of UNC-96 protein levels were
slightly reduced, suggesting that CSN-5 promotes the degradation of UNC-98 and that CSN-5 stabilizes UNC-96. In unc-15
and unc-96 mutants, CSN-5 protein was reduced, implying the existence of feed back regulation from myofibril proteins
to CSN-5 protein levels. Taken together, we found that CSN-5 functions in muscle cells to regulate UNC-98 and -96, two
M-line proteins.
