Acetylornithinase formation

Figure 3 also illustrates acetylornithinase formation in an argR mutant of strain W, followed as described above (plot 3). In this case, comparable results are obtained with or without added arginine. The ratio of the slope of plot 3 to that of plot 2 (repressibility ratio) is of the order of magnitude of 10. This ratio is low compared to that for ornithine transcarbamylase, which has a value of several hundred. 

Fig. 7. Acetylornithinase formation from accumulated mRNA in the orgR strain 961 A) and the argR" strain 977 (5) of Escherichia coii. After accumulation of mRNA by arginine starvation at 37° for 30 minutes, rifampicin (60 jug/ml) is added and allowed to act for 2 minutes. L-Ornithine (open circles), or L-arginine (solid circles), is added (as hydrochlorides, at 0.1 mg/ml) for translation at 37° the addition corresponds to 0 time on the abscissa. From McLellan and Vogel [68].

Fig. 3 Formation of acetylornithinase in Escherichia coli under various regulatory conditions. Plots I and 2 represent formation of the enzyme in the wild-type strain W cultivated without or with added L-arginine hydrochloride (0.2 mg/ml), respectively. Plot 3 represents the formation of the enzyme in the argR mutant W2D (which has an incidental pro marker and is grown in the presence of L-proline, 0.1 mg/ml). Enzyme and total-protein concentrations are expressed per milliliter of extract (1 ml corresponding to 7.5 ml of original culture). The slopes of the plots are the so-called diflFerential rates of enzyme synthesis indicating partial repression (7), full repression (2), and genetic derepression (i).

In addition, analogous experiments were carried out with puromycin (0.03 milligram per milliliter, as dihydrochloride), under conditions of repression or physiological derepression. In this case, no effect on the differential rates of formation of the transaminase, argininosuccinase, or acetylornithinase was observed. These negative findings with puromycin, on the one hand, indicate that the results with the 30 S inhibitors streptomycin and tetracycline are not nonspecific consequences of ribosomal inhibition or lowered growth rate and, on the other hand, would seem to reflect the differences in mode of action between these two inhibitors and puromycin. (A review of the mode of action of ribosomal inhibitors has recently been prepared by Pestka [104].)... 

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