Transcription and RNA Processing

ID #1737

Does poly-A polymerase recognize a consensus sequence to know where to add the poly-A tail. If this is true, can you please explain why a consensus sequence is necessary if the pre-mRNA molecule has one and only one 3' end?

It's not actually the poly-A polymerase that recognizes that conserved region and "knows" where to cut. That's the responsibility of a different molecule which we didn't identify by name. But that molecule must be told where to cut, since this process is also happening concurrently with the termination of transcription. So technically speaking, the actual 3' end of the mRNA is still in the transcription complex! Since that molecule is cutting at some point in the mRNA other than at the end, it has to be directed to the correct spot. Otherwise, there is a risk of making the cut within the protein coding region, which would lead to a mRNA that will have no functional protein translated from it, and then the cell has just wasted its time getting to this point.


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