The Dictyostelium essential light chain is required for myosin function.
A Dictyostelium mutant (7-11) that expresses less than 0.5% of wild-type levels of the myosin essential light chain (EMLC) has been created by overexpression of antisense RNA. Cells from 7-11 contain wild-type levels of the myosin heavy chain (MHC) and regulatory light chain (RMLC). Myosin isolated from 7-11 cells consists of the MHC with the RMLC associated in reduced stoichiometry, and binds to purified actin in an ATP-sensitive fashion. Purified 7-11 myosin displays calcium-activated ATPase activity with a Vmax about 15%-25% of that of wild type, and a Km for ATP of 27 +/- 5 microM versus 83 +/- 30 microM for wild type. At actin concentrations as high as 17 microM, 7-11 myosin displays greatly reduced actin-activated ATPase activity. Phenotypically, 7-11 cells resemble MHC mutants, growing poorly in suspension and becoming large and multinucleate. When starved for multicellular development, 7-11 cells take several hours longer than wild-type cells to aggregate. Although multicellular aggregates eventually form, they fail to develop further. The cells are also unable to cap receptors in response to Con A treatment. Since cells expressing the EMLC are phenotypically similar to MHC null mutants, the EMLC appears necessary for myosin function, at least in part because it is required for normal actin-activated ATPase activity.
Pollenz
R S
RS
Department of Cell, Molecular, and Structural Biology, Northwestern University Medical School, Chicago, Illinois 60611.
Chen
T L
TL
Trivinos-Lagos
L
L
Chisholm
R L
RL
D000199:Actins / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002449:Cell Aggregation; D002460:Cell Line; D003001:Cloning, Molecular; D003599:Cytoskeleton / Q000648:ultrastructure; D004023:Dictyostelium / Q000254:growth & development / Q000378:metabolism*; D005656:Fungal Proteins / Q000378:metabolism; D046911:Macromolecular Substances; D009218:Myosins / Q000378:metabolism* / Q000502:physiology* / Q000648:ultrastructure; D016372:RNA, Antisense; D011940:Receptor Aggregation; D013329:Structure-Activity Relationship
D000199:Actins; D005656:Fungal Proteins; D046911:Macromolecular Substances; D016372:RNA, Antisense; D000255:Adenosine Triphosphate; D009218:Myosins