Saccharomyces cerevisiae IRR1 protein is indirectly involved in colony formation

The ability of a microorganism to adhere to a solid support and to initiate a colony is often the first stage of microbial infections. To date, studie s on S. cerevisiae cell-cell and cell-solid support interactions concerned only cell agglutination during mating and flocculation. Colony formation ha s not been studied before probably because this species is not pathogenic. However, S. cerevisiae can be a convenient model to study this process, tha nks to well-developed genetics and the full knowledge of its nucleotide seq uence. A preliminary characterization of the recently cloned essential IRR1 gene indicated that it may participate in cell-cell/substrate interactions . Here we show that lowering the level of expression of IRR1 (after fusion with a regulatory catalase A gene promoter) affects colony formation and di sturbs zygote formation and spore germination. All these processes involve cell-cell or cell-solid support contacts. The IRR1 protein is localized in the cytosol as verified by immunofluorescence microscopy, and confirmed by cell fractionation and Western blotting. This indicates that Irr1p is not d irectly involved in the cell-solid support adhesion, but may be an element of a communication pathway between the cell and its surroundings. Copyright (C) 1999 John Wiley & Sons, Ltd.