RNA polymerase (RNAP) is the central enzyme of transcription of the genetic information from DNA into RNA. RNAP recognizes four main substrates: ATP, CTP, GTP and UTP. Experimental evidence from the past several years suggests that, besides these four NTPs, other molecules can be used to initiate transcription: (i) ribooligonucleotides (nanoRNAs) and (ii) coenzymes such as NAD+, NADH, dephospho-CoA and FAD. The presence of these molecules at the 5΄ ends of RNAs affects the properties of the RNA. Here, we discuss the expanding portfolio of molecules that can initiate transcription, their mechanism of incorporation, effects on RNA and cellular processes, and we present an outlook toward other possible initiation substrates.

Division of Biomolecular Physics Institute of Physics Faculty of Mathematics and Physics Charles University Ke Karlovu 5 121 16 Prague 2 Czech Republic

Institute of Microbiology Czech Academy of Sciences v v i Vídenská 1083 142 20 Prague 4 Czech Republic

Institute of Organic Chemistry and Biochemistry Czech Academy of Sciences v v i Flemingovo nám 2 166 10 Prague 6 Czech Republic

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