LITERATURE REVEIW
Guides to the Literature
In recent years, several review articles or symposia on RNA poly
merases from prokaryotes (20,36-46) and eukaryotes (47-52), on the
regulatory elements (53,54) and on transcription (55-59), have appeared.
There are several introductory texts (60-62) and collected papers (63-66)
which may be consulted for a more historical background discussion.
General Mechanisms of RNA Synthesis
The synthesis of RNA from DNA is mediated by a DNA dependent RNA
polymerase that uses ribonucleoside triphosphates as precursors. In
general the reaction involves binding of enzyme to DNA template and
the asymmetric transcription of the DNA. RNA synthesis appears to proceed
in the following steps: template binding, chain initiation, chain elon
gation and termination. The RNA polymerase binds to specific initiation
sites (promoter sites) on the DNA in a specific reaction in which the
strands of the DNA are opened over a short local region. Chain initiation
involves the binding of two ribonucleotide triphosphates to the RNA
polymerase followed by elimination of inorganic pyrophosphate to form a
dinucleotide tetraphosphate. The initial nucleotide retains its triphos
phate while each added ribonucleotide triphosphate has its two terminal
phosphates cleaved as pyrophosphate. The direction of elongation is
from 3' hydroxy to 5' phosphate in the DNA, the RNA being made 5' to 3'
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