Nuclear RNA polymerases IV and V

Article By:

Pikaard, Craig S. Department of Biology, Washington University, St. Louis, Missouri.

Last reviewed:2009

DOI:https://doi.org/10.1036/1097-8542.YB090114

In all living cells, genetic information stored as deoxyribonucleic acid (DNA) is copied into ribonucleic acid (RNA) polymers that mediate the chemical transactions of life. For instance, messenger RNAs (mRNAs) carry the codes for proteins to the ribosomes, where proteins are made. So-called noncoding RNAs (ncRNAs) that do not encode proteins also carry out essential functions. For instance, ribosomal RNAs (rRNAs) and transfer RNAs (tRNAs) are essential for protein synthesis. Other ncRNAs guide RNA processing events. Because of the importance of RNA, the enzymes that transcribe DNA into RNA, known as DNA-dependent RNA polymerases, are critical to life. Bacteria and archaea have a single DNA-dependent RNA polymerase. However, in eukaryotic organisms, including fungi, plants, and animals, three different DNA-dependent RNA polymerases, abbreviated as Pol I, Pol II, and Pol III, are essential for cell viability (see table). It was long assumed that eukaryotes use only Pol I, II, and III. However, the sequencing of the Arabidopsis thaliana genome revealed that plants possess two additional nuclear RNA polymerases, Pol IV and Pol V (formerly known as Pol IVa and Pol IVb, respectively) that are not strictly required for cell survival but that specialize in the production of ncRNAs that mediate gene silencing.

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