Response to UV damage by four Escherichia coli K-12 restriction systems

Abstract

To understand the role of restriction in regulating gene flow in bacterial populations, we would like to understand the regulation of restriction enzyme activity. Several antirestriction (restriction alleviation) systems are known that reduce the activity of type I restriction enzymes like EcoKI in vivo. Most of these do not act on type II or type Ill enzymes, but little information is available for the unclassified modificationdependent systems, of which there are three in E. coli K-12. Of particular interest are two physiological controls on type I enzymes: EcoKI restriction is reduced 2 to 3 orders of magnitude following DNA damage, and a similar effect is seen constitutively in Dam-cells. We used the behavior of EcoKI as a control for testing the response to UV treatment of the three endogenous modification-dependent restriction systems of K-12, McrA, McrBC, and Mrr. Two of these were also tested for response to Dam status. We find that all four resident restriction systems show reduced activity following UV treatment, but not in a unified fashion; each response was genetically and physiologically distinct. Possible mechanisms are discussed.

Lack of Regulation of the Modification-Dependent Restriction Enzyme McrBC in Escherichia coli

“…Earlier studies suggested that W3110, the E. coli strain used in these studies, may carry an asyet-uncharacterized restriction system active against T-even phages (13). This may explain some of the differences between our results and those of previous reports (2,7,8). However, as McrB is moderately sensitive to the ClpAP protease, this may also help to reconcile results concerning RA in previous publications (2,7,8 …”

Type I Restriction Systems: Sophisticated Molecular Machines (a Legacy of Bertani and Weigle)

“…It is not known whether RA can be achieved by proteases other than ClpXP or by mechanisms other than proteolysis. RA has been demonstrated for a type III system and for a methylation-dependent system but is not a characteristic of type II systems (81).…”

Diverse Functions of Restriction-Modification Systems in Addition to Cellular Defense

“…To circumvent this burden, the organism appears to control the intracellular enzyme concentration. As shown for E. coli, efficient phage restriction occurs by using about 60 molecules of EcoKI, which would consume ϳ0.2% of the total ATP pool (86,87).…”