Flexible Frame

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Is the open reading frame of a gene flexible?

I am slighty confused about when and where a reading frame can begin and end in a gene. I have read that an insertion of a "T" can cause a premature stop codon "TGA" in this situation:

AGA----> A-T-GA

But that from this a start codon (ATG) can initate a new reading frame.
I would have thought that this would not be possible as the "A" preceding the TGA stop codon is part of the truncated gene. How can it also represent the beginning of a new read?
EDIT: I should have pointed it out more clearly. The original set-up was:

CGA-GAC

The "T" is inserted between the two codons resulting ina frameshift.

CGA-TGA-CXX

I am curious that the "A" preceding the stop codon, can also be the first letter of a start codon (ATG) for a new reading frame.

I guess it depends on the context that the T insertion appears in. If it is in the middle of an ORF then you have already assembled the RNA transcription machinery and it reaches a stop codon. Of course the RNA polymerase is not responsible for the transcription, just the translation. So it keeps going until it find the necessary termination sequences and you have a'bad' message. The problem with the premature termination dies not happen until you get translation. For that case, I think you just end up with a stop when the thing is translated.

But, if you get an insertion like you describe at the 5' end (front end) of an ORF, then when the ribosome binds and starts looking for the first ATG, they could recognize the second ATG and start translating from there. Of course you end up with the same problems downstream, namely, you are in the wrong reading frame and pretty soon you will run into a stop codon in this alternate reading frame too.

So, in the first case you end up with a stop codon and the end of the story. In the second case you end up with the possibility of initiation at a new stop codon, but one that is off from the proper reading frame by 1bp and so you get junk in the translation.

Flexible Frame - Kraj tebe