Polarized growth and organelle segregation in yeast: the tracks, motors, and receptors

Abstract

In yeast, growth and organelle segregation requires formin-dependent assembly of polarized actin cables. These tracks are used by myosin Vs to deliver secretory vesicles for cell growth, organelles for their segregation, and mRNA for fate determination. Several specific receptors have been identified that interact with the cargo-binding tails of the myosin Vs. A recent study implicates specific degradation in the bud of the vacuolar receptor, Vac17, as a mechanism for cell cycle-regulated segregation of this organelle.

Figure 1.

Diagram summarizing the myosin V–based mechanisms of organelle transport. (1) Formins are localized and activated (Bni1 at the bud tip and Bnr1 at the bud neck), which drive the assembly of polarized actin cables. (2) Actin cables are stabilized by tropomyosin (blue) and cross-linking proteins (e.g., fimbrin, green). (3) Myo2 transports post-Golgi secretory vesicles into the bud. (4) Nuclear orientation involves Myo2-dependent transport of Kar9/Bim1 into the bud. (5) Specific mRNAs are selected by the She2/3 complex and transported into the bud by Myo4. (6) Vacuolar elements are moved by Myo2 into the bud through an interaction with Vac8/17. After transport into the bud, Vac17 is degraded (not depicted).