Limits...
Transposon-mediated directed mutation controlled by DNA binding proteins in Escherichia coli.

Saier MH, Zhang Z - Front Microbiol (2014)

View Article: PubMed Central - PubMed

Affiliation: Division of Biological Sciences, Department of Molecular Biology, University of California at San Diego La Jolla, CA, USA.

AUTOMATICALLY GENERATED EXCERPT
Please rate it.

The concept of directed mutation, defined as genetic change that is specifically induced by the stress conditions that the mutation relieves (Cairns et al., ), challenges this principle (Foster, ; Rosenberg, ; Wright, )... Part of the justifiable skepticism concerning directed mutation resulted from experiments that were purported to demonstrate this phenomenon, but were subsequently shown to be explainable by classical genetics (Roth et al., )... The numbers of Glp cells arising was 10-fold higher in the crp glpR double mutant than in the crp mutant when glycerol was absent... In the presence of glycerol, the loss of GlpR was without effect... There are four GlpR binding sites, O1–O4, in the upstream glpFK operon regulatory region (see Figure 1A), identified by DNA footprinting (Freedberg and Lin, ; Zeng et al., )... We mutated the far upstream site (O1) and the far downstream site (O4) so they no longer could bind GlpR, and compared the effects on glpFK expression using a lacZ reporter gene fusion construct vs. mutation rate to Glp during growth in LB medium... Initial attempts in our laboratory and elsewhere to isolate such mutants in a wild type genetic background proved unsuccessful (Ibarra et al., ; Honisch et al., ; Fong et al., ; Zhang and Saier,, unpublished observations; Cheng et al., )... Since crp mutants are not found in nature, this brought into question the suggestion that our discovery of directed mutation in a crp mutant of E. coli was relevant to the wild type situation, and hence whether it had actually evolved under the pressures of natural selection... Although the mechanism was not established, the frequency of IS5 insertion clearly increased under swarming conditions in soft agar compared to growth in liquid medium or on solid agar plates where swarming does not occur (Wang and Wood, )... We have confirmed and extended their results (Zhang et al., )... Directed mutation has been defined as genetic change that is specifically induced by the stress conditions that the mutation relieves, but until recently, in no case had such a mechanism been established... This example of directed mutation could therefore have been selected for during evolution... It appears to be a genuine example of directed mutation, with mutations arising at a greater rate under conditions that allow benefit to the organism... The fact that mutation rate is influenced by the presence of glycerol in a process mediated by the glycerol repressor, and by cAMP in a process mediated by CRP, provides mechanistic explanations for IS5-mediated directed mutational control.

No MeSH data available.


Related in: MedlinePlus

Schematic diagram illustrating dual GlpR-mediated/cAMP-CRP-mediated control of (right) the level of glpFK transcription and (left) the rate of IS5 hopping into the activating site upstream of the glpFK promoter (directed mutation). With GlpR bound to its operators (O1–O4) (in the presence of GlpR and the absence of glycerol), transcription and IS5 hopping both occur at low rates. When GlpR is not bound to its operators (in the absence of GlpR or in the presence of glycerol), both transcriptional initiation and IS5 hopping increase about 10×. Binding of GlpR to operator O1 preferentially blocks IS5 insertion, while binding of GlpR to operator O4 preferentially blocks transcription as indicated. Binding of cAMP-CRP to its transcriptional activating sites, CrpI and CrpII, similarly inhibits IS5 hopping even though binding of this complex promotes glpFK transcription. Glucose inhibits IS5 insertion by a mechanism independent of glycerol, GlpR, cAMP, and CRP. (, activation; , inhibition or repression).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4117983&req=5

Figure 2: Schematic diagram illustrating dual GlpR-mediated/cAMP-CRP-mediated control of (right) the level of glpFK transcription and (left) the rate of IS5 hopping into the activating site upstream of the glpFK promoter (directed mutation). With GlpR bound to its operators (O1–O4) (in the presence of GlpR and the absence of glycerol), transcription and IS5 hopping both occur at low rates. When GlpR is not bound to its operators (in the absence of GlpR or in the presence of glycerol), both transcriptional initiation and IS5 hopping increase about 10×. Binding of GlpR to operator O1 preferentially blocks IS5 insertion, while binding of GlpR to operator O4 preferentially blocks transcription as indicated. Binding of cAMP-CRP to its transcriptional activating sites, CrpI and CrpII, similarly inhibits IS5 hopping even though binding of this complex promotes glpFK transcription. Glucose inhibits IS5 insertion by a mechanism independent of glycerol, GlpR, cAMP, and CRP. (, activation; , inhibition or repression).

Mentions: The mechanism of IS5-mediated glpFK promoter activation in wild type cells provides relief from starvation when glycerol is present and a cAMP-depressing toxic substance, such as 2-deoxyglucose, is simultaneously present. Such non-metabolizable sugar derivatives are synthesized by many organisms and therefore are present in nature. This example of directed mutation could therefore have been selected for during evolution. It appears to be a genuine example of directed mutation, with mutations arising at a greater rate under conditions that allow benefit to the organism. The fact that mutation rate is influenced by the presence of glycerol in a process mediated by the glycerol repressor, and by cAMP in a process mediated by CRP, provides mechanistic explanations for IS5-mediated directed mutational control. This mechanism, illustrated in Figure 2, allows rationalization of the presence of four GlpR binding sites and two CRP binding sites in the control region of the glpFK operon. Our studies also provide the rationale for the evolution of this elaborate mechanism of gene activation.


Transposon-mediated directed mutation controlled by DNA binding proteins in Escherichia coli.

Saier MH, Zhang Z - Front Microbiol (2014)

Schematic diagram illustrating dual GlpR-mediated/cAMP-CRP-mediated control of (right) the level of glpFK transcription and (left) the rate of IS5 hopping into the activating site upstream of the glpFK promoter (directed mutation). With GlpR bound to its operators (O1–O4) (in the presence of GlpR and the absence of glycerol), transcription and IS5 hopping both occur at low rates. When GlpR is not bound to its operators (in the absence of GlpR or in the presence of glycerol), both transcriptional initiation and IS5 hopping increase about 10×. Binding of GlpR to operator O1 preferentially blocks IS5 insertion, while binding of GlpR to operator O4 preferentially blocks transcription as indicated. Binding of cAMP-CRP to its transcriptional activating sites, CrpI and CrpII, similarly inhibits IS5 hopping even though binding of this complex promotes glpFK transcription. Glucose inhibits IS5 insertion by a mechanism independent of glycerol, GlpR, cAMP, and CRP. (, activation; , inhibition or repression).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4117983&req=5

Figure 2: Schematic diagram illustrating dual GlpR-mediated/cAMP-CRP-mediated control of (right) the level of glpFK transcription and (left) the rate of IS5 hopping into the activating site upstream of the glpFK promoter (directed mutation). With GlpR bound to its operators (O1–O4) (in the presence of GlpR and the absence of glycerol), transcription and IS5 hopping both occur at low rates. When GlpR is not bound to its operators (in the absence of GlpR or in the presence of glycerol), both transcriptional initiation and IS5 hopping increase about 10×. Binding of GlpR to operator O1 preferentially blocks IS5 insertion, while binding of GlpR to operator O4 preferentially blocks transcription as indicated. Binding of cAMP-CRP to its transcriptional activating sites, CrpI and CrpII, similarly inhibits IS5 hopping even though binding of this complex promotes glpFK transcription. Glucose inhibits IS5 insertion by a mechanism independent of glycerol, GlpR, cAMP, and CRP. (, activation; , inhibition or repression).
Mentions: The mechanism of IS5-mediated glpFK promoter activation in wild type cells provides relief from starvation when glycerol is present and a cAMP-depressing toxic substance, such as 2-deoxyglucose, is simultaneously present. Such non-metabolizable sugar derivatives are synthesized by many organisms and therefore are present in nature. This example of directed mutation could therefore have been selected for during evolution. It appears to be a genuine example of directed mutation, with mutations arising at a greater rate under conditions that allow benefit to the organism. The fact that mutation rate is influenced by the presence of glycerol in a process mediated by the glycerol repressor, and by cAMP in a process mediated by CRP, provides mechanistic explanations for IS5-mediated directed mutational control. This mechanism, illustrated in Figure 2, allows rationalization of the presence of four GlpR binding sites and two CRP binding sites in the control region of the glpFK operon. Our studies also provide the rationale for the evolution of this elaborate mechanism of gene activation.

View Article: PubMed Central - PubMed

Affiliation: Division of Biological Sciences, Department of Molecular Biology, University of California at San Diego La Jolla, CA, USA.

AUTOMATICALLY GENERATED EXCERPT
Please rate it.

The concept of directed mutation, defined as genetic change that is specifically induced by the stress conditions that the mutation relieves (Cairns et al., ), challenges this principle (Foster, ; Rosenberg, ; Wright, )... Part of the justifiable skepticism concerning directed mutation resulted from experiments that were purported to demonstrate this phenomenon, but were subsequently shown to be explainable by classical genetics (Roth et al., )... The numbers of Glp cells arising was 10-fold higher in the crp glpR double mutant than in the crp mutant when glycerol was absent... In the presence of glycerol, the loss of GlpR was without effect... There are four GlpR binding sites, O1–O4, in the upstream glpFK operon regulatory region (see Figure 1A), identified by DNA footprinting (Freedberg and Lin, ; Zeng et al., )... We mutated the far upstream site (O1) and the far downstream site (O4) so they no longer could bind GlpR, and compared the effects on glpFK expression using a lacZ reporter gene fusion construct vs. mutation rate to Glp during growth in LB medium... Initial attempts in our laboratory and elsewhere to isolate such mutants in a wild type genetic background proved unsuccessful (Ibarra et al., ; Honisch et al., ; Fong et al., ; Zhang and Saier,, unpublished observations; Cheng et al., )... Since crp mutants are not found in nature, this brought into question the suggestion that our discovery of directed mutation in a crp mutant of E. coli was relevant to the wild type situation, and hence whether it had actually evolved under the pressures of natural selection... Although the mechanism was not established, the frequency of IS5 insertion clearly increased under swarming conditions in soft agar compared to growth in liquid medium or on solid agar plates where swarming does not occur (Wang and Wood, )... We have confirmed and extended their results (Zhang et al., )... Directed mutation has been defined as genetic change that is specifically induced by the stress conditions that the mutation relieves, but until recently, in no case had such a mechanism been established... This example of directed mutation could therefore have been selected for during evolution... It appears to be a genuine example of directed mutation, with mutations arising at a greater rate under conditions that allow benefit to the organism... The fact that mutation rate is influenced by the presence of glycerol in a process mediated by the glycerol repressor, and by cAMP in a process mediated by CRP, provides mechanistic explanations for IS5-mediated directed mutational control.

No MeSH data available.


Related in: MedlinePlus