Dinucleoside polyphosphates act as 5'-RNA caps in bacteria.

Area of Science:

• Molecular Biology
• Biochemistry
• RNA Biology

Background:

• Dinucleoside polyphosphates (Np_nNs) have been known for over 50 years, but their biological functions remain largely unknown.
• The precise roles and mechanisms of Np_nNs in cellular processes require further elucidation.

Purpose of the Study:

• To investigate the function of Np_nNs in prokaryotic RNA biology, specifically in Escherichia coli.
• To determine if Np_nNs act as RNA caps and their involvement in transcription initiation and regulation.

Main Methods:

• Investigated Np_nNs as substrates for T7 and E. coli RNA polymerases (RNAPs).
• Assessed the ability of E. coli enzymes RNA 5'-pyrophosphohydrolase (RppH) and bis(5'-nucleosyl)-tetraphosphatase (ApaH) to remove Np_nN-caps from RNA.
• Compared the cleavage activity of RppH and ApaH on both methylated and non-methylated Np_nN-caps.

Main Results:

• Demonstrated that both methylated and non-methylated Np_nNs serve as functional RNA caps in E. coli.
• Showed that Np_nNs are efficient substrates for RNAPs, facilitating transcription initiation.
• Confirmed that ApaH can cleave all Np_nN-caps, while RppH is specific for non-methylated caps, indicating methylation's role in RNA stability.

Conclusions:

• Np_nNs represent a novel class of RNA caps in prokaryotes, influencing RNA structure and function.
• RNA cap methylation by Np_nNs provides an additional regulatory layer for RNA stability.
• The incorporation of small molecules like Np_nNs into RNA impacts cellular metabolism and RNA turnover.