Functional effects of adaptive mutations in a gene network polymorphism.

(A) NCR genes are altered in expression in clones recovered from ammonium-limited conditions. Only genes having at least one observation with log₂ ratio >|1.5| were included (29/38 NCR genes [71]). Genes and samples are hierarchically clustered using centered correlation and complete linkage. (B) Three independently acquired GAT1 mutations found in a single ammonium-limitation adapted population are clustered in the zinc finger DNA binding domain of the encoded protein. The wild type GAT1 protein sequence was queried using the Protein Model Portal database [72]. (C) Two different point mutations in MEP2 found in ammonium-limitation adapted clones change the identical codon within a putative trans-membrane domain. Domain information was obtained from SGD database (http://www.yeastgenome.org/). (D) GAT1 and LST4 likely regulate the production and delivery of MEP2 to the plasma membrane at the transcriptional and post-translational level, respectively.