Question about 5' Methyl Capping of RNA

[Captopril]

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Okay so in FA and Kaplan, it says that the methyl capping occurs inside the nucleus (along with the rest of the post-transcriptional modifications like splicing and Poly-A tail).

However, UWorld has about 2-3 questions on the topic and all of them say Methyl Capping occurs outside of the nucleus.

Can anyone provide me with a concrete answer?

 

[McGillGrad]

It is my understanding that the capping is required for export from the nucleus. It is different in viruses I believe.

 

[Sol Rosenberg]

Odd that UWorld would say that, since every source I have ever read (I just double-checked one of them) states that the 5' cap is not only involved in targeting the mRNA for export from the nucleus, but is also added before the transcript is complete (in the nucleus.)

 

[StIGMA]

Capping is co-transcriptional along with splicing, polyadenylation, etc.

In the cytoplasm, de-capping (for mRNA decay) and re-capping may occur.

See:
http://www.ncbi.nlm.nih.gov/pubmed/...med_ResultsPanel.Pubmed_RVDocSum&ordinalpos=1

Schoenberg DR, Maquat LE. "Re-capping the message."
Trends Biochem Sci. 2009 Sep;34(9):435-42. Epub 2009 Sep 2.

 

[Captopril]

Capping is co-transcriptional along with splicing, polyadenylation, etc.

In the cytoplasm, de-capping (for mRNA decay) and re-capping may occur.

Maybe UW is referring to this? I'll stick with inside the nucleus for the test though.

Thanks everyone.

 

[robmcc1]

I remember seeing this in UW as well - it seemed that it was referring to just a part of the capping process that occurred outside the nucleus; i.e. some capping occurs inside the nucleus then just the methylation of the cap occurs in the cytosol.

 

[HazomboL]

The guanyl capping happens inside the nucleus..
It is the methylation of this guanyl group that occurs cytoplasmically..
So, technically the capping happens in the nucleus and is modified in the cytoplasm..

Very evil from the UWorld, though. 🙂

 

[HazomboL]

The guanyl capping happens inside the nucleus..
It is the methylation of this guanyl group that occurs cytoplasmically..
So, technically the capping happens in the nucleus and is modified in the cytoplasm..

Very evil from the UWorld, though. 🙂

 

[HazomboL]

The guanyl capping happens inside the nucleus..
It is the methylation of this guanyl group that occurs cytoplasmically..
So, technically the capping happens in the nucleus and is modified in the cytoplasm..

Very evil from the UWorld, though. 🙂

 

[Captopril]

I remember seeing this in UW as well - it seemed that it was referring to just a part of the capping process that occurred outside the nucleus; i.e. some capping occurs inside the nucleus then just the methylation of the cap occurs in the cytosol.

The guanyl capping happens inside the nucleus..
It is the methylation of this guanyl group that occurs cytoplasmically..
So, technically the capping happens in the nucleus and is modified in the cytoplasm..

Very evil from the UWorld, though. 🙂

This sounds really familiar. Those question writers show no mercy. Thanks guys, will write this into FA asap