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Vol. 17, Issue 4, 1812-1821, April 2006

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Regulated Phosphorylation of Budding Yeast's Essential Myosin V Heavy Chain, Myo2p

Aster Legesse-Miller ^*, Sheng Zhang  , Felipe H. Santiago-Tirado ^*, Colleen K. Van Pelt , and Anthony Bretscher ^*

^* Department of Molecular Biology and Genetics, Biotechnology Building, Cornell University, Ithaca, NY 14853; Advion BioSciences, Ithaca, NY 14850

Submitted September 20, 2005; Revised December 28, 2005; Accepted February 1, 2006
Monitoring Editor: Kerry Bloom

The tail of the yeast myosin V encoded by Myo2p is known to bind several receptors for cargo delivery along polarized actin cables. However, it is not known how Myo2p activity is regulated or how it selects between cargos. Here we show that Myo2p is reversibly phosphorylated in vivo. A short peptide at the N-terminal end of the cargo-binding domain contains three residues contributing to single or doubly phosphorylated species. We confirm that the tail consists of two proteolytically resistant subdomains and identify a functionally important region N-terminal to sudomain 1 that includes the phosphorylation sites. Mutagenesis of the phosphorylation sites to alanine abolished a mobility shift diagnostic of phosphorylation, whereas mutagenesis to glutamic acid produced the shift and the formation of an additional phosphorylated species. These substitutions did not affect overall cell growth. However, one of the sites is predicted to be a substrate of cAMP-dependent protein kinase (PKA), and yeast expressing Myo2p with alanine substitutions is resistant to otherwise lethal overexpression of PKA, whereas the glutamic acid mutant is supersensitive to overexpression of PKA. These results suggest that in yeast, Myo2p is subject to phosphoregulation involving a PKA-related signaling pathway.

The online version of this article contains supplemental material at MBC Online (http://www.molbiolcell.org).

Present address: Biotechnology Resource Center, Biotechnology Building, Cornell University, Ithaca, NY 14853.

Address correspondence to: Anthony P. Bretscher (apb5{at}cornell.edu).

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