Constitutive Activation of Endocytosis by Mutation ofmyoA, the Myosin I Gene of Aspergillus nidulans*
Abstract
Class I myosins function in cell motility, intracellular vesicle trafficking and endocytosis. Recently, it was shown that class I myosins are phosphorylated by a member of the p21-activated kinase (PAK) family. PAK phosphorylates a conserved serine or threonine residue in the myosin heavy chain. Phosphorylation at this site is required for maximal activation of the actin-activated Mg2+-ATPase activity in vitro. This serine or threonine residue is conserved in all known class I myosins of microbial origin and in the human and mouse class VI myosins. We have investigated the in vivo significance of this phosphorylation by mutating serine 371 of the class I myosin heavy chain gene myoA of Aspergillus nidulans. Mutation to glutamic acid, which mimics phosphorylation and therefore activation of the myosin, results in an accumulation of membranes in growing hyphae. This accumulation of membranes results from an activation of endocytosis. In contrast, mutation of serine 371 to alanine had no discernible effect on endocytosis. These studies are the first to demonstrate the in vivo significance of a regulatory phosphorylation on a class I myosin. Furthermore, our results suggest that MYOA has two functions, one dependent and one independent of phosphorylation.
Footnotes
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↵* This work was supported by a grant from NIGMS, National Institutes of Health (to G. S. M.) and by a National Institutes of Health training grant (to R. A. Y.).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵‡ To whom correspondence should be addressed: Dept. of Cell Biology, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030. Tel.: 713-798-4756; Fax: 713-798-7799; E-mail: gsmay{at}bcm.tmc.edu.
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↵1 The abbreviations used are: PAK, p21-activated kinase; PCR, polymerase chain reaction; bp, base pair(s); PBS, phosphate-buffered saline; DIC, differential interference contrast; FM 4–64,N-(3-triethylammoniumpropyl)-4-(p-diethylaminophenyl-hexitrienyl)pyridinium dibromide.
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↵2 H. Brzeska and E. Korn, personal communication.
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- Received January 12, 1998.
- Revision received February 25, 1998.
- The American Society for Biochemistry and Molecular Biology, Inc.
