The regulation and properties of the galactose transport system in Escherichia coli K12.
نویسنده
چکیده
This study of galactose-induced galactose transport in Escherichia coli K12 showed that in most strains two transport systems having the properties of “galactose permease” and “P-methyl galactoside permease” are responsible for the observed transport. Several strains contain only the galactose transport system but still grow normally on galactose. The regulation of this system was shown to be very similar to that of the galactose operon. That is, it is induced by galactose, shows only a slight repression by glucose, and is under the control of the galactose regulator gene. The only differences between the regulation of the galactose transport system and that of the galactose enzymes are the level of induction (4-fold for the galactose transport system U~TSUS 15-fold for the galactose enzymes) and the fact that the galactose transport system is not under the control of the galactose operator locus. The P-methyl galactoside transport system is not regulated by either galactose regulatory gene in agreement with the work of Lengeler el al. (LENGELER, J., HERMANN, K. O., UNSOLD, H. J. & Boos, W. (1971) Eur. J. Biochem. 19, 457-470). Galactose-binding protein is not essential for the activity of the galactose transport system as there is no correspondence between the level of the two. In fact, the galactose transport system is present at near normal levels under conditions where there is no measurable binding protein activity. Although the galactose and P-methyl galactoside transport systems have different genetic loci and are controlled by different regulatory systems, they do not function independently when they are both present in the same cell. Rather, they interact in a complex way that results in the rate of transport by the P-methyl galactoside system being reduced at high galactose concentrations and the K, of transport by the galactose system being reduced 3-fold.
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ورودعنوان ژورنال:
- The Journal of biological chemistry
دوره 249 2 شماره
صفحات -
تاریخ انتشار 1974