RNA polymerase is an enzyme that synthesizes RNA molecules by copying a DNA sequence during the process called transcription. It binds to a specific region on the DNA called the promoter, unwinds the DNA strands, and uses one strand as a template to assemble a complementary RNA strand by adding RNA nucleotides (adenosine, cytosine, guanine, and uracil) in a 5' to 3' direction
. In addition to initiating transcription, RNA polymerase guides nucleotide positioning, facilitates elongation of the RNA chain, proofreads the RNA transcript, and recognizes termination signals to end transcription properly
. In eukaryotes, there are multiple types of RNA polymerase with specialized functions:
- RNA polymerase I synthesizes most ribosomal RNA (rRNA),
- RNA polymerase II transcribes protein-coding genes into messenger RNA (mRNA) and also produces microRNA (miRNA),
- RNA polymerase III transcribes other small RNAs
The RNA produced can be coding (mRNA) for protein synthesis or non-coding (such as tRNA, rRNA, miRNA) with various regulatory and catalytic roles
. In summary, RNA polymerase is essential for gene expression, converting genetic information stored in DNA into RNA, which then directs protein synthesis or regulates gene activity
