Chitin synthesis regulation, resistance to Congo red
RCR proteins are ER membrane proteins that regulate chitin deposition in fungal cell walls. Although chitin, a linear polymer of beta-1,4-linked N-acetylglucosamine, constitutes only 2% of the cell wall it plays a vital role in the overall protection of the cell wall against stress, noxious chemicals and osmotic pressure changes. Congo red is a cell wall-disrupting benzidine-type dye extensively used in many cell wall mutant studies that specifically targets chitin in yeast cells and inhibits growth. RCR proteins render the yeasts resistant to Congo red by diminishing the content of chitin in the cell wall. RCR proteins are probably regulating chitin synthase III interact directly with ubiquitin ligase Rsp5, and the VPEY motif is necessary for this, via interaction with the WW domains of Rsp5.