To measure the effect of metabolic mutations on carbon flux polarity, competent cells of the GM1514 strain that contains lacZ downstream from the gapB promoter at the amyE locus were transformed with the total DNA extracted from strains carrying metabolic mutations (168 Pgi::spc, 501 77, GM1501, GTD040 and DGRM18, 25).
These results are consistent with another study that found high levels of recombination in pgi [25].
WS-4 is WS wspR::mini-Tn5; WS-12 is WS pgi::mini-Tn5, and WS-13 is WS wssB::mini-Tn5 [2].
These charge-changing substitutions do not appear to be derived from differential neutral evolution of base composition or codon usage between Pgi-1 and Pgi-2 genes, as demonstrated by the fact that GC content and codon usage frequencies are not significantly different between Pgi-1 and Pgi-2 (GC content: P = 0.0782, Mann-Whitney U test, n = 12; rank order of codon usage: rs = 0.9509, n = 64).
The fact that these duplicated Pgi-1 and Pgi-2 genes in fishes are expressed in different organs [ 12, 15] implies that these fish-specific duplicate Pgi genes are subfunctionalized with respect to their expression, and are thus good candidates for the model of subfunctionalized genes.
In contrast, strong evidence for selection has been found for two well-studied loci, phosphoglucose isomerase (Pgi; [ 11, 13]) and alcohol dehydrogenase (Adh; [ 4, 18]) in a wide range of organisms, and for other loci on a smaller scale [e.g., [ 7, 8]].
The specific glucose uptake rate was very high for the reference strain (11.3 mmol h−1 gcdw−1) but in the range of previously reported values (Toya et al. 2010) and significantly lower for the Δ pfkA mutant (4.0 mmol h−1 gcdw−1) and the Δ pgi mutant (2.7 mmol h−1 gcdw−1).
Similarly, clines in allele frequencies of Pgi-1 in the leaf beetle Chrysomela aeneicollis were linked to enzyme kinetic performance across ecologically-relevant temperatures, providing strong evidence of temperature-driven selection [ 61].
In contrast, the teleost Pgi-1 gene was expressed mainly in internal organs, including the liver, heart, gill, brain, and kidney, and weakly in the muscle, whereas Pgi-2 was expressed mainly in the heart and muscle.
