I've been pondering over this exam question for the past week or so. A situation was described: transcriptional levels of an unknown gene was quantified under wild-type conditions. Then, the gene was removed from the chromosome, and expression dropped to zero. However, re-introduction of the gene on a plasmid, together with its native promoter, yielded a two-fold increase in expression, compared to the wild-type.

I answered that perhaps the gene was under some sort of topological regulation, which would be chromosome-dependent. My supervisor said this was probably too complicated, though I might still get the marks. I'm genuinely curious about the answer though, and don't want to wait another two weeks until the model answers are released.

Anyone genetics students on jsp?

It's been a bit since I took biochemistry, and by extension had genetics in any class, but how about if it was only added back with the promoter and not with its repressor?

That definitely sounds plausible, and much more simplistic than my explanation... I probably overcomplicated it

I don't think it's right though, as that would be complicated to remove a repressor and not affect the promoter.

Another might be if it just has greater access to proteins since it's in a plasmid and not in a chromosome, which has histones and other junk that is going to keep it from being interacted with by proteins.

Would you say that my topology explanation would be a reasonable guess? As far as I know there was no precise answer to the question, it just asked for a reasonable answer

What is topological regulation?

I am pretty sure its effects based on somethings position/location relative to something elses position/location.

Not really my field, but i find this all very interesting and wanted to chime in.

This post was edited by Ep0ch on Jun 18 2017 02:50pm

Some bacterial promoters, when the DNA is supercoiled, can have their -35 and -10 elements improperly aligned on the double helix, so the RNA polymerase holoenzyme cannot bind - DNA gyrase (iirc) relieves the supercoiling to properly align the RNA polymerase binding sites, allowing transcription.

My logic was that since plasmids are not supercoiled, any regulation attributable to supercoiling wouldn't be observed.



If you mean the -35 element's position relative to the -10 element's position, you're right

It sounds like the simplest answer, maybe not so specific, but access by proteins seems like it would be correct.

Although Thor's solution is impractical I would most definitely expect such an answer at an exam. 'Tis all theory, after all >.<