EXPRESSION OF A MYOSIN REGULATORY LIGHT-CHAIN PHOSPHORYLATION SITE MUTANT COMPLEMENTS THE CYTOKINESIS AND DEVELOPMENTAL DEFECTS OF DICTYOSTELIUM RMLC NULL-CELLS

Citation
Bd. Ostrow et al., EXPRESSION OF A MYOSIN REGULATORY LIGHT-CHAIN PHOSPHORYLATION SITE MUTANT COMPLEMENTS THE CYTOKINESIS AND DEVELOPMENTAL DEFECTS OF DICTYOSTELIUM RMLC NULL-CELLS, The Journal of cell biology, 127(6), 1994, pp. 1945-1955
Citations number
74
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Cell Biology
Journal title
ISSN journal
0021-9525
Volume
127
Issue
6
Year of publication
1994
Part
2
Pages
1945 - 1955
Database
ISI
SICI code
0021-9525(1994)127:6<1945:EOAMRL>2.0.ZU;2-9
Abstract
In a number of systems phosphorylation of the regulatory light chain ( RMLC) of myosin regulates the activity of myosin. In smooth muscle and vertebrate nonmuscle systems RMLC phosphorylation is required for con tractile activity. In Dictyostelium discoideum phosphorylation of the RMLC regulates both ATPase activity and motor function. We have determ ined the site of phosphorylation on the Dictyostelium RMLC and used si te-directed mutagenesis to replace the phosphorylated serine with an a lanine. The mutant light chain was then expressed in RMLC null Dictyos telium cells (mLCR(-)) from an actin promoter on an integrating vector . The mutant RMLC was expressed at high levels and associated with the myosin heavy chain. RMLC bearing a ser13ala substitution was not phos phorylated in vitro by purified myosin light chain kinase, nor could p hosphate be detected on the mutant RMLC in vivo. The mutant myosin had reduced actin-activated ATPase activity, comparable to fully dephosph orylated myosin. Unexpectedly, expression of the mutant RMLC rescued t he primary phenotypic defects of the mlcR(-) cells to the same extent as did expression of wild-type RMLC. These results suggest that while phosphorylation of the Dictyostelium RMLC appears to be tightly regula ted in vivo, it is not essential for myosin-dependent cellular functio ns.