Component of the outer cell wall layer required for stability of the cell wall and specifically for cell wall rigidity. Covalently attached to the cell wall. Expression varies during the cell-cycle with a peak at the beginning of G1. Expression increases in hypoxic and acidic conditions and is down-regulated during the switch from yeast to hyphal growth and under low-iron conditions. The promoter contains E-box consensus sequences (CANNTG) suggesting that PIR1 is directly regulated by EFG1. Expression is also regulated by ACE2, HOG1, and RIM101. The PIR1/2/3 repeats are required for covalent linkage to the cell wall. Covalently linked to beta-1,3-glucan of the inner cell wall layer via an alkali-sensitive ester linkage between the gamma-carboxyl group of glutamic acids, arising from specific glutamines within the PIR1/2/3 repeats, and hydroxyl groups of glucoses of beta-1,3-glucan chains. Highly O-glycosylated by PMT1 and contains one N-mannosylated chain. Increases sensitivity to calcofluor white and Congo red. Belongs to the PIR protein family.