Does Yck1/2 phosphorylation affect septin‐dependent compartmentalization in yeast cells?

Abstract

Yeast casein kinase 1 (CK1) proteins Yck1 and 2 are redundant and essential plasma membrane‐associated protein kinases in budding yeast that are required for cellular morphogenesis and cytokinesis. We identified Ser548 in Shs1 as a potential Yck1/2 phosphorylation site using a comparative phosphoproteomic approach. Shs1 is one of five septin proteins that are essential for several aspects of cell division, including mother‐bud membrane compartmentalization. Septin activity is regulated by phosphorylation, and septin ring formation does not occur properly in cells expressing the low activity yck2ts mutant protein. We generated cells expressing mutant Shs1 proteins altered at the putative Yck2 phosphorylation site and tested the ability of these cells to maintain membrane compartmentalization. Cells expressing S548A or S548E Shs1 maintained appropriate endoplasmic reticulum membrane separation during bud formation, as assessed by low fluorescence recovery after photobleaching of GFP‐tagged Sec61. Similar results were observed in cells expressing the yckts protein. We conclude that phosphorylation of S548 on Shs1 is not required for this function of the septin ring. Supported by NSF grant MCB‐0517204.