Why are some colonies blue in my T-vector self-ligation experiment?

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Discussion Overview

The discussion revolves around the occurrence of blue colonies in a T-vector self-ligation experiment, specifically focusing on the mechanisms behind blue-white screening and the potential for self-ligation of the T-vector. Participants explore various factors that could contribute to the unexpected blue colonies, including the linearization process, ligation steps, and the behavior of the bacteria.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether the T-overhangs could self-ligate or if incomplete preparatory steps could lead to circularized plasmids remaining.
  • Another participant inquires about the method of linearization of the T-vector and the specifics of the ligation reaction performed on the blank control.
  • A participant expresses uncertainty about the self-ligation capability of the vector once T-overhangs are present, suggesting that blue colonies must indicate self-ligation.
  • One participant asserts that the vector should not self-ligate with T-overhangs and interprets the absence of colonies in the blank control as evidence against self-ligation.
  • Another participant acknowledges a lack of understanding of the preparation process, attributing the blue colonies to potential issues in that step.

Areas of Agreement / Disagreement

Participants express differing views on the mechanisms leading to blue colonies, with some suggesting self-ligation while others argue against it based on the presence of T-overhangs. The discussion remains unresolved regarding the exact cause of the blue colonies.

Contextual Notes

Participants note limitations in their understanding of the linearization and ligation processes, which may affect their interpretations of the results. There is also uncertainty regarding the completeness of the preparatory steps and the implications for the experiment's outcomes.

Who May Find This Useful

This discussion may be useful for researchers and students involved in molecular biology experiments, particularly those working with cloning techniques and vector design.

nobahar
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Hello!

I conducted a transformation experiment and plated the bacteria on antibiotic agar with blue-white screening. The plasmid I used was a linearized T-vector. The insert with A overhangs would insert into the lacZ gene. If it is successfully inserted, white colonies should form. However, apparently it's possible to get blue colonies. I don't understand why. Can the T overhangs self-ligate somehow? Or would it be something in the preparatory steps for constructing the vector - say, the prep was not complete and some circularized plasmids remained or the t overhangs were not added successfully? I was also thinking that maybe the bacteria could remove overhangs?
I included a circularized control, is it merely to cover the possibility of contamination? I personally don't think so, I had a 'blank' colony (no insert included but t-vector was), on which nothing grew. Although this doesn't actually tell me much.

Anyone got any ideas.
Many thanks.
 
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How did you linearize your T-vector? For your blank control, did you perform the ligation reaction or did you just transform the linearized vector without a ligation step?
 
Ygggdrasil said:
How did you linearize your T-vector? For your blank control, did you perform the ligation reaction or did you just transform the linearized vector without a ligation step?

Hi Ygg, thanks for the response. Thats the thing, I was simply given a linearized vector, no explanation, so I don't know the process for it. For the control, I subjeted iot to the ligation as if there was some insert, but I just didn;t include an insert in the mix. It went through all the same processes otherwise. he blue colonies have to be self-ligation, since its the only way for the bacteria to survive and the colonies to be blue, so it must be in the prep step that I din;t do. Can they even self-ligate once the overhangs are on?

Thanks for the response.
 
Yes, the vector should not be able to self-ligate once it has the t-overhangs on it. The fact that you see no colonies in your blank is also a good indication that no self-ligation is going on. Blue/white screening is useful for distinguishing re-circularized vectors from plasmids containing inserts, and so the screening seems unnecessary because your vector is designed to prevent self-ligation.
 
Thanks Ygg, it must be in the prep step then. I haven't been taught how that works so I wasn;t aware of the procedure. Thanks again!
 

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