The multiple functions of a cell wall stress sensor.
Gordon Ford, Katherine Wilson, Douglas Stirling
School of
Life Sciences, University of Dundee, MSI/WTB Complex, Dundee, DD1 5EH,
UK
In S. cerevisiae a group of type I transmembrane proteins
that includes Wsc1p/Slg1p/Hcs77p and Mid2p is proposed to sense and
signal cell surface stress associated with cellular morphogenesis or
caused by high temperature, low osmolarity or cell wall damage.
Collectively these so-called stress sensors perform an essential
function that involves activation of the PKC1-MPK1 cell integrity
pathway to cause cell wall remodeling. In addition, individual stress
sensors have specific functions. To understand the molecular basis of
this, we have been examining the properties of Mid2p. Unlike the other
stress sensors, a mid2 null mutant is highly resistant to
calcofluor white, reflecting the role of Mid2p in stress-induced chitin
synthesis, and shows a severe loss of viability on prolonged exposure to
mating pheromone. As we find that neither of these phenotypes is
mediated by the PKC1-MPK1 pathway, Mid2p must have other effectors.
Truncation of a large portion of the C-terminal cytoplasmic domain of
Mid2p does not affect viability in mating pheromone. In contrast, an
intact cytoplasmic domain is necessary for wild type sensitivity to
calcofluor white, indicating the importance of this region for stress-induced chitin synthesis. Therefore, these two functions of Mid2p are
likely to proceed via distinct mechanisms. Consistent with this view,
chitin deposition at the base of mating projections which is also
promoted by Mid2p, is not required for pheromone treated cells to remain
viable.
Return to YGM 2002 Home at SGD