- Suppression of sorbitol dependence in a strain bearing a mutation in the SRB1/PSA1/VIG9 gene encoding GDP-mannose pyrophosphorylase by PDE2 overexpression suggests a role for the Ras/cAMP signal-transduction pathway in the control of yeast cell-wall biogenesis. Tomlin, G.C., Hamilton, G.E., Gardner, D.C., Walmsley, R.M., Stateva, L.I., Oliver, S.G. Microbiology (Reading, Engl.) (2000)