DNAdependent RNA polymerase A

transcriptase mediating the transference of the information encoded in the base sequence in DNA to an analogous base sequence in mRNA. The RNA chain is initiated at a specific site on the DNA, the 'promoter region', and transcription is terminated at another specific site, the 'terminator region'. These are specific signals in the DNA template recognized by the transcription apparatus. In animal cells, three distinct DNA-dependent RNA polymerases are found, known usually as forms I, II and III (although sometimes as forms A, B and C) which mediate the synthesis from DNA of ribosomal RNA, mRNA and tRNA (as well as 5S ribosomal RNA and some families of short dispersed repetitive nucleotide sequences), respectively. Only form II, and to a minor extent form III, are inhibited by a-amanitin, which binds to the enzymes. Actinomycin D inhibits the function of all three enzymes by binding to the DNA template. Some viruses, notably the poxviruses, contain their own virus-encoded, virion-bound, DNA-dependent RNA polymerase which mediates the synthesis of virus-specific mRNA early in infection.

Synonyms: DNA transcriptase; RNA tran-scriptase.

0 0

Post a comment