Abstract
In Escherichia coli, the role of lacA, the third gene of the
lactose operon, has remained an enigma. I suggest that
its role is the consequence of the need for cells to have
safety valves that protect them from the osmotic effect
created by their permeases. Safety valves allow them to
cope with the buildup of osmotic pressure under accidental
transient conditions. Multidrug resistance (MDR)
efflux, thus named because of our anthropocentrism, is
ubiquitous. Yet, the formation of simple leaks would
result in futile influx/efflux cycles. Versatile modification
enzymes with low sensitivity solve the problem if the
modified metabolite is the one exported by MDR permeases.
This may account for the pervasive presence of
acetyl-transferases, such as LacA, associated to acetyl-metabolite
exporters. This scenario of constraints
imposed by efficient influx of metabolites provides us
with a model that should be followed when constructing
synthetic cells.