Regulation of Myo5p function by phosphorylation

The Saccharomyces cerevisiae type I myosins Myo3p and Myo5p are involved in endocytosis and in the polarization of the actin cytoskeleton. In vitro, p21-activated kinases (PAKs) can phosphorylate a single serine in the myosin-I head domain, referred to as TEDS site, thereby activating the myosin-I ATPase. This work demonstrates that phosphorylation of the Myo5p TEDS site is required for two myosin-I in vivo functions in yeast, endocytosis and actin cytoskeleton polarization. However, the yeast PAKs Ste20p, Cla4p and Skm1p and their activator Cdc42p, while important for actin cytoskeleton polarity, are not required for the uptake step of endocytosis. An in vitro screen identified several other kinases as possible TEDS site kinases including the sphingoid base-activated kinase Pkh2p. Preliminary results support a model in which Pkh2p and its paralogue Pkh1p are part of a signalling cascade that leads to TEDS site phosphorylation and thus myosin-I activation for endocytosis. A second important feature of fungal myosins-I is their ability to induce actin polymerization through the Arp2/3 complex. Within this work, Myo5p serine 1205, located N-terminal to the sequence that interacts with and activates the Arp2/3 complex, was identified as a phosphorylation site for casein kinase II (CKII). This phosphorylation event appears to negatively regulate myosin-I-induced actin polymerization. The fact that mutation of one catalytically active subunit of CKII increases the Ą-factor internalization rate, points to a inhibitory role of this kinase in endocytosis, which might be a direct consequence of the inhibitory effect of myosin-I tail phosphorylation on Arp2/3 dependent actin polymerization.

Level thesis:degree_level

thesis.doctoral

Grantor dc:publisher

Universität Heidelberg

Year

2003

Author dc:creator

• Großhans, Bianka Lucretia

Contributors dc:contributor

• Wieland, Felix

Repository record source_url

http://www.ub.uni-heidelberg.de/archiv/3554

OAI identifier oai:identifier

oai:archiv.ub.uni-heidelberg.de:3554