A second mRNA polymerase!

[Gibsons]

Text

Transcription of mammalian messenger RNAs by a nuclear RNA polymerase of mitochondrial origin

Julia E. Kravchenko1,2, Igor B. Rogozin3, Eugene V. Koonin3 and Peter M. Chumakov1,2
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Transcription of eukaryotic genes is performed by three nuclear RNA polymerases, of which RNA polymerase II is thought to be solely responsible for the synthesis of messenger RNAs1. Here we show that transcription of some mRNAs in humans and rodents is mediated by a previously unknown single-polypeptide nuclear RNA polymerase (spRNAP-IV). spRNAP-IV is expressed from an alternative transcript of the mitochondrial RNA polymerase gene (POLRMT). The spRNAP-IV lacks 262 amino-terminal amino acids of mitochondrial RNA polymerase, including the mitochondrial-targeting signal, and localizes to the nucleus. Transcription by spRNAP-IV is resistant to the RNA polymease II inhibitor alpha-amanitin but is sensitive to short interfering RNA specific for the POLRMT gene. The promoters for spRNAP-IV differ substantially from those used by RNA polymerase II, do not respond to transcriptional enhancers and contain a common functional sequence motif.

This might not be of general interest, but it nearly floored me to read it.

There have been three and only three RNA polymerases since roughly the 70s, and RNA Pol II has been everything in mRNA transcription. RNA transcription, particularly mRNA, has been studied endlessly. And just now they found a new enzyme that makes mRNA.. and it's mitochondrial! There are going to be a ton of papers on this in the near future - mapping out the genes it makes, how (or if) they are different from Pol II genes, how the genes are regulated... It's present in rats and humans, so it's also probably in most mammals, or placental ones anyway. I haven't read the full article yet (forgot to xerox it (yes, my institution has a license 😛 )), so I don't know yet how many species they tested, so it could be widespread or just restricted to mammals.

Exciting stuff if you're a biology geek. 🙂

 

[Slappy00]

so this new pol is just an alternate transcript of a known polymerase gene that lacking the signal peptides that would otherwise confine it to the mitochondria migrates to the nucleus where it's fuction is yet to be explored?

Question is what it transcribes and of what relevance it is? I dont think that this will shake the pillars of molecular biology but it is noteworthy ( the abstract is seems to infer that it is the same polymerase, but without a guidence system). Looking at the transcripts and promotors would be interesting, but im not burning my molecular biology book just yet.

 

[Gibsons]

Originally posted by: Slappy00

so this new pol is just an alternate transcript of a known polymerase gene that lacking the signal peptides that would otherwise confine it to the mitochondria migrates to the nucleus where it's fuction is yet to be explored?

If I read your question correctly, yes...

Question is what it transcribes and of what relevance it is?

Yep. I'm sure people have looked for the promoter sequence described in the paper in the sequence databases, maybe the authors put it in the paper. There are also some interesting questions on how the RNA is processed; they don't indicate if the messages are capped, spliced or polyadenyated.

I dont think that this will shake the pillars of molecular biology but it is noteworthy ( the abstract is seems to infer that it is the same polymerase, but without a guidence system). Looking at the transcripts and promotors would be interesting, but im not burning my molecular biology book just yet.

Right, it could be somewhat unimportant in the grand scheme of things, and it's not overthrowing all the work on Pol II. But given how intensive the effort on RNA transcription has been over the 25 years, I think it's quite surprising.

 

[Slappy00]

Im waiting for someone to discover how amino acid sequence corrilates to tertiary structure. at my old job it was a pia to harvest/purify protiens and then concentrate and crystalize them, not to mention difract them with xrays and fianally get beam time at teh APS. If we know how protein sequence related to structure that would really usher in a new golden age of science (much like in the 60's and early 1900's. Thats what I am waiting for myself, although enviormental conditions and side-chain interactions are so complex that its going to be awhile. Sequence does corilate to structure and then function... I just hope I am still alive to see science crack the code.

The polymerase is a bit odd though, i mean if its a functional pol from the mitochondria it was never origionally intentioned to work in the host cell's DNA (assuming it has always been around, but maybe it was created specificaly for that purpose) , so the question is: What caused this to happen? Maybe there is some need for a particualr protein that the mitochondiral DNA cannot produce, or maybe its a cytoplasmic protien that somehow benefits the mitchondira but it would be too difficult to transport or maybe needs to be localized in the host DNA...

and it was published in Nature.... wish I could get a publication there 🙁