Escherichia coli polypeptide controlled by the lon (capR) ATP hydrolysis-dependent protease and possibly involved in cell division

Mutation in the gene lon (capR) of Escherichia coli K-12 causes conditional inhibition of cell division. Two-dimensional gel electrophoresis was used to compare polypeptides from isogenic capR+ and capR strains. One polypeptide was present in the capR strain but absent in the wild-type strain, and it was proteolyzed when the pure capR+ protease was added to the capR extract. This polypeptide could only be detected in the capR strain when cell division was inhibited, and its synthesis was independent of the SOS response.     

DNA-stimulated ATPase activity on the lon (CapR) protein.

The gene product of the pleiotropic lon (also called capR) locus in Escherichia coli, the CapR protein, is an ATP hydrolysis-dependent protease and a nonspecific nucleic acid-binding protein. We demonstrated that it is also a DNA-stimulated adenosine triphosphatase (ATPase). This new activity is distinct from the protease-associated ATPase activity and occurs in the absence of proteolytic substrate. The reaction requires the presence of a divalent cation and has a pH optimum of 8.0. The products of the reaction are ADP and inorganic phosphate. No adenylation or phosphorylation of the DNA or proteins was detected. The maximum rate of ATP hydrolysis occurs in the presence of supercoiled (form I) DNA. Relaxed circles (form II), double-stranded DNA, and single-stranded DNA are less effective in promoting ATPase activity, whereas RNA is inactive. The DNA-stimulated ATPase activity is inhibited by a mutationally altered form of the CapR protein called the CapR9 protein. The interaction of the CapR and CapR9 subunits suggests that this enzymatic activity of the CapR protein is oligomeric in the presence of DNA. Our in vitro experiments indicate a possible role for nucleic acids in the regulation of all lon (capR) activity.     

IN VIVO INHIBITION OF RAT BRAIN PROTEIN SYNTHESIS BY d-AMPHETAMINE

Abstract— Between 1 and 4 h after rats received a single injection of d-amphetamine (15 mg/kg)(when brain polysomes are known to be disaggregated), the in vivo incorporation of [¹⁴C]lysine into trichloroacetic acid-precipitable brain protein was reduced by 28–48%. Incorporation of the ¹⁴C label into the protein present in a 100,000 g supernatant extract of whole brain was similarly reduced (by 44%). Amphetamine administration suppressed protein synthesis in rat cerebral cortex, cerebellum, hypothalamus, striatum, and brainstem to an equivalent extent. The drug did not significantly affect lysine pool sizes measured in these brain regions; thus the reduced incorporation of labeled lysine was not the result of an isotope dilution effect. We therefore conclude that the brain polysome disaggregation resulting from amphetamine administration is associated with decreased in vivo synthesis of some brain proteins.