It has been more than 50 years since the discovery of dinucleoside polyphosphates (Np n Ns) and yet their roles and mechanisms of action remain unclear. Here, we show that both methylated and non-methylated Np n Ns serve as RNA caps in Escherichia coli. Np n Ns are excellent substrates for T7 and E. coli RNA polymerases (RNAPs) and efficiently initiate transcription. We demonstrate, that the E. coli enzymes RNA 5′-pyrophosphohydrolase (RppH) and bis(5′-nucleosyl)-tetraphosphatase (ApaH) are able to remove the Np n N-caps from RNA. ApaH is able to cleave all Np n N-caps, while RppH is unable to cleave the methylated forms suggesting that the methylation adds an additional layer to RNA stability regulation. Our work introduces a different perspective on the chemical structure of RNA in prokaryotes and on the role of RNA caps. We bring evidence that small molecules, such as Np n Ns are incorporated into RNA and may thus influence the cellular metabolism and RNA turnover.

Helquat dyes are the first helicene-like cationic styryl dyes obtained as separate enantiomers. Their remarkable chiroptical properties are due to the unique combination of a cationic hemicyanine chromophore and a helicene-like motif. The magnitude of the ECD response and the pH switching along with their positioning in the visible region are unprecedented among helicenoids.

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