SummaryCell morphogenesis is a complex process that depends on cytoskeleton and membrane organization, intracellular signalling and vesicular trafficking. The rod shape of the fission yeast Schizosaccharomyces pombe and the availability of powerful genetic tools make this species an excellent model to study cell morphology. Here we have investigated the function of the conserved Kin1 kinase. Kin1-GFP associates dynamically with the plasma membrane at sites of active cell surface remodelling and is present in the membrane fraction. Kin1D null cells show severe defects in cell wall structure and are unable to maintain a rod shape. To explore Kin1 primary function, we constructed an ATP analoguesensitive allele kin1-as1. Kin1 inhibition primarily promotes delocalization of plasma membraneassociated markers of actively growing cell surface regions. Kin1 itself is depolarized and its mobility is strongly reduced. Subsequently, amorphous cell wall material accumulates at the cell surface, a phenotype that is dependent on vesicular trafficking, and the cell wall integrity mitogen-activated protein kinase pathway is activated. Deletion of cell wall integrity mitogen-activated protein kinase components reduces kin1D hypersensitivity to stresses such as those induced by Calcofluor white and SDS. We propose that Kin1 is required for a tight link between the plasma membrane and the cell wall.

Actively maintained close appositions between organelle membranes, also known as contact sites, enable the efficient transfer of biomolecules between cellular compartments. Several such sites have been described as well as their tethering machineries. Despite these advances we are still far from a comprehensive understanding of the function and regulation of most contact sites. To systematically characterize contact site proteomes, we established a high-throughput screening approach in Saccharomyces cerevisiae based on co-localization imaging. We imaged split fluorescence reporters for six different contact sites, several of which are poorly characterized, on the background of 1165 strains expressing a mCherry-tagged yeast protein that has a cellular punctate distribution (a hallmark of contact sites), under regulation of the strong TEF2 promoter. By scoring both co-localization events and effects on reporter size and abundance, we discovered over 100 new potential contact site residents and effectors in yeast. Focusing on several of the newly identified residents, we identified three homologs of Vps13 and Atg2 that are residents of multiple contact sites. These proteins share their lipid transport domain, thus expanding this family of lipid transporters. Analysis of another candidate, Ypr097w, which we now call Lec1 (Lipid-droplet Ergosterol Cortex 1), revealed that this previously uncharacterized protein dynamically shifts between lipid droplets and the cell cortex, and plays a role in regulation of ergosterol distribution in the cell. Overall, our analysis expands the universe of contact site residents and effectors and creates a rich database to mine for new functions, tethers, and regulators.