Expression of a myosin regulatory light chain phosphorylation site mutant complements the cytokinesis and developmental defects of Dictyostelium RMLC null cells

Bruce D. Ostrow, Pengxin Chen, Rex L. Chisholm*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

76 Scopus citations

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 contractile activity. In Dictyostelium discoideum phosphorylation of the RMLC regulates both ATPase activity and motor function. We have determined the site of phosphorylation on the Dictyostelium RMLC and used site-directed mutagenesis to replace the phosphorylated serine with an alanine. The mutant light chain was then expressed in RMLC null Dictyostelium 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 phosphorylated in vitro by purified myosin light chain kinase, nor could phosphate be detected on the mutant RMLC in vivo. The mutant myosin had reduced actin-activated ATPase activity, comparable to fully dephosphorylated myosin. Unexpectedly, expression of the mutant RMLC rescued the 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 regulated in vivo, it is not essential for myosin-dependent cellular functions.

Original languageEnglish (US)
Pages (from-to)1945-1955
Number of pages11
JournalJournal of Cell Biology
Volume127
Issue number6 II
DOIs
StatePublished - Dec 1994

ASJC Scopus subject areas

  • Cell Biology

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