Table 4.

Suggested Changes to Model Structure Based on the Gene Deletion Study


ORF

Gene

Reason for false predictiona

Suggested change and comments
YPL188W POSS Mod Change the model so that only Pos5p can provide NADPH in mitochondria
YMR267W PPA2 Mod Force the model to use Ppa2p instead of the cytoplasmic isoforms by restricting phosphate transport out of the mitochondria.
YMR202W ERG2 Mod Modify the interconversion between zymosterol and ergosterol biosynthesis to require ERG2.
YLR056W ERG3 Mod See ERG2.
YML008C ERG6 Mod See ERG2.
YDR178W SDH4 Iso Make Sdh4p a nonessential part of the succinate dehydrogenase complex.
YML123C PHO84 Iso There are multiple alternative isozymes for the phosphate transporters, but Pho84p should be the dominant one.
YBR069C TAT1 Iso There are multiple alternative isozymes for amino acid transporters in the model, but they need to be made less efficient than Tat1p.
YLR081W GAL2 Iso Model includes other isozymes (HXT genes) that are not nearly as efficient for gal transport, so disabling their gal transport ability should result in a correct prediction.
YMR105C PGM2 Iso Pgm2p is major isoform of phosphoglucomutase; do not allow the minor isoform (Pgm1p) to fully compensate for loss of Pgm2p.
YHR137W ARO9 Iso Aro8p should be able to compensate for ARO9 deletion on minimal media; modify the gene-protein-reaction association to reflect this.
YGL125W MET13 Iso Met13p is the dominant isozyme; do not allow isozyme (Met12p) to compensate fully for the loss of Met13p.
YHR046C INM1 Iso Add the gene product of YDR287W as an isozyme for Inm1p.
YHR001WA QCR10 Iso This subunit should be made a nonessential part of the cytochrome bc1 complex since it only plays a structural role.
YFR033C QCR6 Iso Deletion of QCR6 does not have significant effect on the formation or stability of cytochrome bc complex so that it should not play an essential role in complex formation.
YKL067W YNK1 Iso Null mutant retains 10% of nucleoside diphosphate kinase activity. Sources of remaining enzyme activity are unknown. Reaction without gene associations should be added to the model to represent these unidentified enzymes.
YLR304C ACO1 Iso The isozyme coded by YJL200C should not be able to fully compensate for ACO1 deletion.
YNL052W COX5A Iso Cox5Ap is the dominant isoform; Cox5Bp should not be able to fully compensate.
YKL148C SDH1 Iso Sdh1p should not be considered to be an essential part of the succinate dehydrogenase complex.
YGL008C PMA1 Iso This is the major isoform of the cytosolic ATPase, but in the model a minor isoform (which contains Pma2p instead of Pma1p) can compensate for the function. Do not allow the minor isoform to fully compensate for the loss of the major isoform.
YLR342W FKS1 Iso There are three alternate isozymes in the model, but Fks1p should be made the dominant isozyme.
YHR183W GND1 Iso This is the major isozyme (80% of activity); other isozymes should be made less efficient.
YLR044C PDC1 Iso There are three alternate isozymes in the model, but PDC1 deletion alone is sufficient to reduce pyruvate decarboxylase activity significantly enough to result in a slow growth phenotype. Should have Pdc1p as the major isozyme.
YJR148W BAT2 Iso BAT2 single deletion should not be lethal as there is a mitochondrial isozyme (Bat1p); double deletion should be lethal. Bat1p currently does not catalyze valine transamination so this functionality should be added.
YCL009C ILV6 Iso Ilv6p is the regulatory subunit of phenylalanine transaminase. This subunit should be made nonessential for the enzymatic function.
YAL038W CDC19 Reg Pyk2p isozyme should only be expressed under conditions of very low glycolytic flux.
YOL086C
ADH1
Reg
This isozyme (out of five) should be the only one active under severely glucose repressed conditions.

a The reasons for false predictions have been classified as model structure-related (Mod), gene-protein-reaction association-related (Iso), or transcriptional regulation related (Reg). See Supplemental materials as well as http://systemsbiology.ucsd.edu for more details.