Reciprocal Regulation of Anaerobic and Aerobic Cell Wall Mannoprotein Gene Expression in Saccharomyces cerevisiae

Abstract

The DAN/TIR genes encode nine cell wall mannoproteins in Saccharomyces cerevisiae which are expressed during anaerobiosis (DAN1, DAN2, DAN3, DAN4, TIR1, TIR2, TIR3, TIR4, and TIP1). Most are expressed within an hour of an anaerobic shift, but DAN2 and DAN3 are expressed after about 3 h. At the same time, CWP1 and CWP2, the genes encoding the major mannoproteins, are down-regulated, suggesting that there is a programmed remodeling of the cell wall in which Cwp1 and Cwp2 are replaced by nine anaerobic counterparts. TIP1, TIR1, TIR2, and TIR4 are also induced during cold shock. Correspondingly, CWP1 is downregulated during cold shock. As reported elsewhere, Mox4 is a heme-inhibited activator, and Mot3 is a heme-induced repressor of the DAN/TIR genes (but not of TIP1). We show that CWP2 (but not CWP1) is controlled by the same factors, but in reverse fashion-primarily by Mot3 (which can function as either an activator or repressor) but also by Mox4, accounting for the reciprocal regulation of the two groups of genes. Disruptions of TIR1, TIR3, or TIR4 prevent anaerobic growth, indicating that each protein is essential for anaerobic adaptation. The Dan/Tir and Cwp proteins are homologous, with the greatest similarities shown within three subgroups: the Dan proteins, the Tip and Tir proteins, and, more distantly, the Cwp proteins. The clustering of homology corresponds to differences in expression: the Tip and Tir proteins are expressed during hypoxia and cold shock, the Dan proteins are more stringently repressed by oxygen and insensitive to cold shock, and the Cwp proteins are oppositely regulated by oxygen and temperature.The cell wall of Saccharomyces cerevisiae is a rigid structure which determines cell morphology and also serves as a protective barrier, providing mechanical protection and enabling selective uptake of macromolecules (1a, 4, 7). A major component of the cell wall is mannoprotein, comprising about 40% of its mass. Mannoproteins are believed to be determinants of cell wall permeability (31), and certain ones are also essential for developmental events such as mating and transition to hyphal growth (18,24). Some mannoproteins can be extracted from the cell wall with detergent; others are covalently bound but can be released with glucanase (7). Proteins in the latter category have common features, including a region rich in serine and threonine, a glycosylphosphatidylinositol (GPI) anchor attachment signal at C termini (3,8), and an endoplasmic reticulum localization sequence; several also have a PAU domain. This segment of about 100 amino acids is shared among a group of proteins known as "seripauperins" (29).The Cwp2 mannoprotein (28) is one of the most abundant proteins of the cell wall and is believed to play a role in its stabilization, along with another homologous constituent, Cwp1 (23, 27, 28). While Cwp1 and Cwp2 are expressed under normal growth conditions, other mannoproteins are expressed in response to environmental stress. The most extensive response is the induction of several homologou...

Genes with internal repeats require the THO complex for transcription

“…Cold shock and anaerobic growth experiments were based on previously described protocols (29). For cold shock, cultures were grown at 30°C to OD 600 1.0 and then shifted to 15°C for 90 min; strains were grown hypoxically on YPD plates supplemented with 0.5% Tween 80 and 20 g͞ml ergosterol (Sigma, St. Louis, MO) and placed in a hypoxic chamber with an AnaeroPack sachet (Mitsubishi Gas Chemical America, New York, NY) for 3 days at 30°C.…”

“…TIR1 is a cell wall gene encoded by 765 nt, 261 of which are internal tandem repeats. The gene is required for hypoxic growth and is induced by cold shock as well as by low oxygen levels (29). The level of TIR1 mRNA was measured in a Tho ϩ strain and in Tho Ϫ mutants after a 90-min cold shock at 15°C.…”

Uncoupling reproduction from metabolism extends chronological lifespan in yeast

“…S6C). Conspicuously up-regulated are subtelomeric loci in the PAU seripauperin gene family, whose functions are unknown, and subtelomeric loci in the TIR cell wall mannoprotein gene family; both families have been described as being activated during anaerobic alcoholic fermentation (32,33). Down-regulated clusters illuminate how immobilization uncouples reproduction from metabolism.…”

Genomic analysis of the hierarchical structure of regulatory networks

“…In particular, the expression of MOT3, a top-level TF involved in aerobic growth, is activated by heme and oxygen (33,34) (Fig. 3), representing the decision phase.…”