RNA Polymerase in Escherichia coli

The enzyme that synthesizes RNA is called RNA polymerase, and the most extensively studied one was isolated from E. coli. The molecular weight of this enzyme is about 470,000 Da, and it has a multisuhunit structure. Five different types of suhunits, designated a, CO, P, P, and o, have heen identified. The actual composition of the enzyme is 0t2(0pP o. The o-suhunit is rather loosely hound to the rest of the enzyme (the 0t2(0pp portion), which is called the core enzyme. The holoenzyme consists of all the suhunits, including the a-suhunit. 

The a-suhunit is involved in the recognition of specihc promoters, whereas the P , P -, a-, and CO-suhunits combine to make the active site for polymerization. The mechanism of the polymerization reaction is an active area of research. 

The core enzyme of RNA polymerase is catalytically active but lacks specificity. The core enzyme alone would transcribe both strands of DNA when only one strand contains the information in the gene. The holoenzyme of RNA polymerase binds to specific DNA sequences and transcribes only the correct strand. The essential role of the O-subunit is recognition of the promoter locus (a DNA sequence that signals the start of RNA transcription see Section 11.3). The loosely bound O-subunit is released after transcription begins and about 10 nucleotides have been added to the RNA chain. Prokaryotes can have more 

RNA polymerase uses the template strand of DNA to make an RNA transcript that has the same sequence as the nontemplate DNA strand, with the exception that T is replaced by U. If this RNA is mRNA, it can later be translated to protein. 

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R. Lange, D. Fischer and R. Hengge-Aronis (1995). Identification of transcriptional start sites and the role of ppGpp in the expression of rpoS, the structural gene for the sigma S subunit of RNA polymerase in Escherichia coli. J. Bacteriol., 177, 4676-4680. 

Regulation of Biosynthesis of the DNA-Dependent RNA Polymerase in Escherichia coli Hans Matzura... 

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