Dynamic localization of protein phosphatase type 1 in the mitotic cell cycle of Saccharomyces cerevisiae

Protein phosphatase type I (PP1), encoded by the single essential gene GLC7 in Saccharomyces cerevisiae, functions in diverse cellular processes. To i dentify in vivo subcellular location(s) where these processes take place, w e used a functional green fluorescent protein (GFP)-Glc7p fusion protein. T ime-lapse fluorescence microscopy revealed GFP-Glc7p localizes predominantl y in the nucleus throughout the mitotic cell cycle, with the highest concen trations in the nucleolus. GFP-Glc7p was also observed in a ring at the bud neck, which was dependent upon functional septins. Supporting a role for G lc7p in bud site selection, a glc7-129 mutant displayed a random budding pa ttern. In at-factor treated cells, GFP-Glc7p was located at the base of mat ing projections, again in a septin-dependent manner. At the start of anapha se, GFP-Glc7p accumulated at the spindle pole bodies and remained there unt il cytokinesis. After anaphase, GFP-Glc7p became concentrated in a ring tha t colocalized with the actomyosin ring. A GFP-Glc7-129 fusion was defective in localizing to the bud neck and SPBs. Together, these results identify s ites of Glc7p function and suggest Glc7p activity is regulated through dyna mic changes in its location.