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VOL. 73 (4), 901-925, 2007 ROLES OF PROTEIN PHOSPHATASE TYPE 1...

endocytic vesicles. Dis2.EGFPN dots were moving from the cell
cortex towards the interior of the cell for a short distance. This
pattern of movement was very similar to that recently described in
budding yeast for proteins involved in endocytic internalisation. In
basis of the analysis of the motility of fusions between endocytotic
proteins and GFP a model for the early endocytotic pathway has
been proposed (59-61) (Figure 5).

FIGURE 5. Pathway for the association of receptors, adaptors and actin
during endocytic internalisation. First, Sla1, Sla2, Pan1 and Las17 assemble in
a nonmotile complex at the plasma membrane. Then, actin, Abp1, and the Arp2/3

complex are recruited, whereupon the complex containing Sla1, Sla2 and Pan1
slowly moves away from the plasma membrane, towards the interior of the cell.
The early patch components are disassembled during this slow movement phase.
The patches containing only late components change then to a fast movement
phase during which the late components are disassembled. Actin polymerisation is
required for the movement of the presumed endocytic vesicles and its associated

protein complex, and for subsequent disassembly of the complex. The early
components of the patches (Sla1, Sla2 and Pan1) are likely to be disassembled as
a response to phosphorylation by the Ark1 and Prk1 kinases. This phosphorylation

might disrupt the association of Sla1 with Pan1. If Pan1 and Sla1 are
phosphorylated and then lost from the complex, dephosphorylation might allow
their re-incorporation into cortical complexes. This dephosphoryaltion might be

carry out by the Glc7-Scd5 complex. Adapted from Kaksonen et al. (59).

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