Dykhuizen D E, Hartl D L
Genetics. 1983 Sep;105(1):1-18. doi: 10.1093/genetics/105.1.1.
Five alleles representing three electromorphs of phosphoglucose isomerase (PGI) have been transferred from natural isolates of E. coli into the genetic background of E. coli K12 and examined for their effect on growth rate in chemostats limited for glucose or fructose. With glucose limitation, all alleles are selectively neutral or nearly neutral within the limit of resolution of the technique, whether the genetic background is nonmutant or whether it contains a deletion of the locus of glucose-6-phosphate dehydrogenase, the enzyme that provides an alternative metabolic pathway for the substrate of PGI. With fructose limitation, one of the naturally occurring alleles has a small but reproducible detrimental effect on growth rate. A kinetic difference in this detrimental allozyme, apparently relating to an inhibition constant, has been observed in some, but not all, lots of substrate, and a similar difference has also been noted in one of the rare electromorphs that could not be transferred into E. coli K12. These results support a model of genetic variation in which the alleles are neutral or nearly neutral in the prevailing environment but have a potential for selection that can be expressed under the appropriate conditions of environment or genetic background. This hypothesis is discussed in the context of allozyme polymorphisms observed in other organisms.
已将代表磷酸葡萄糖异构酶（PGI）三种电泳形态的五个等位基因从大肠杆菌的自然分离株转移到大肠杆菌K12的遗传背景中，并检测了它们在葡萄糖或果糖受限的恒化器中对生长速率的影响。在葡萄糖受限的情况下，无论遗传背景是非突变型，还是包含葡萄糖-6-磷酸脱氢酶基因座的缺失（该酶为PGI的底物提供了一条替代代谢途径），在该技术的分辨率范围内，所有等位基因均具有选择性中性或接近中性。在果糖受限的情况下，一个天然存在的等位基因对生长速率有微小但可重复的不利影响。在部分（但不是全部）底物批次中观察到了这种有害同工酶的动力学差异，这显然与抑制常数有关，并且在无法转移到大肠杆菌K12中的一种罕见电泳形态中也注意到了类似差异。这些结果支持了一种遗传变异模型，即等位基因在当前环境中是中性或接近中性，但具有在适当的环境或遗传背景条件下表现出的选择潜力。在其他生物体中观察到的同工酶多态性的背景下讨论了这一假设。
