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Ribonucleoprotein-dependent localization of the yeast class V myosin Myo4p
Claudia Kruse1, Andreas Jaedicke, Joel Beaudouin
1Zentrum für Molekulare Biologie, Universität Heidelberg, D-69120 Heidelberg, Germany.
Abstract:
Class V myosins are motor proteins with functions in vesicle transport, organelle segregation, and RNA localization. Although they have been extensively studied, only little is known about the regulation of their spatial distribution. Here we demonstrate that a GFP fusion protein of the budding yeast class V myosin Myo4p accumulates at the bud cortex and is a component of highly dynamic cortical particles. Bud-specific enrichment depends on Myo4p's association with its cargo, a ribonucleoprotein complex containing the RNA-binding protein She2p. Cortical accumulation of Myo4p at the bud tip can be explained by a transient retention mechanism that requires SHE2 and, apparently, localized mRNAs bound to She2p. A mutant She2 protein that is unable to recognize its cognate target mRNA, ASH1, fails to localize Myo4p. Mutant She2p accumulates inside the nucleus, indicating that She2p shuttles between the nucleus and cytoplasm and is exported in an RNA-dependent manner. Consistently, inhibition of nuclear mRNA export results in nuclear accumulation of She2p and cytoplasmic Myo4p mislocalization. Loss of She2p can be complemented by direct targeting of a heterologous lacZ mRNA to a complex of Myo4p and its associated adaptor She3p, suggesting that She2p's function in Myo4p targeting is to link an mRNA to the motor complex.
Insights
Budding yeast myosin Myo4p localization to the bud cortex depends on its cargo, the She2p ribonucleoprotein complex. RNA binding by She2p is crucial for Myo4p transport and retention at the bud tip.
Area of Science:
- Cell biology
- Molecular genetics
- Biochemistry
Background:
- Class V myosins are motor proteins essential for intracellular transport processes, including vesicle transport, organelle segregation, and RNA localization.
- The spatial distribution and regulatory mechanisms governing class V myosins, particularly Myo4p in budding yeast, remain incompletely understood.
Purpose of the Study:
- To investigate the regulation of the spatial distribution of the budding yeast class V myosin, Myo4p.
- To elucidate the role of Myo4p's cargo in its localization to the bud cortex.
Main Methods:
- Utilized a GFP fusion protein of Myo4p to track its localization in budding yeast.
- Investigated the interaction between Myo4p, its adaptor She3p, and the RNA-binding protein She2p.
- Employed mutant strains of She2p and manipulated mRNA export to assess their impact on Myo4p localization.
Main Results:
- Myo4p accumulates at the bud cortex as part of dynamic cortical particles, indicating specific spatial regulation.
- Bud-specific localization of Myo4p is dependent on its association with the She2p-containing ribonucleoprotein complex.
- Myo4p's cortical accumulation is mediated by a transient retention mechanism requiring She2p and its bound mRNAs, such as ASH1 mRNA.
- A mutant She2p defective in ASH1 mRNA binding fails to localize Myo4p, and accumulates in the nucleus, suggesting RNA-dependent nuclear export.
- Inhibition of nuclear mRNA export leads to nuclear She2p accumulation and cytoplasmic Myo4p mislocalization.
Conclusions:
- She2p acts as a crucial link between Myo4p and its mRNA cargo, facilitating Myo4p's transport and localization.
- Myo4p localization is regulated by a mechanism involving transient retention at the bud tip, dependent on RNA binding by She2p.
- She2p shuttles between the nucleus and cytoplasm in an RNA-dependent manner, influencing Myo4p localization.