RNA
Polymerases
in
Prokaryotes -
In
prokaryotes
a
single
RNA
polymerase
enzyme
controls
the
synthesis
of
all
the
different
types
of
cellular
RNA.
In
E.coli
for
example,
the
same
RNA
polymerase
catalyses
the
synthesis
of
mRNA,
tRNA
and
rRNA.The
entire
RNA
polymerase
enzyme
(holozyme)
consists
of
a
core
enzyme
and
a
sigma
(a)
factor.
In
Escherchia
coli
and
Anacytis
(blue
green
alga)
the
core
enzyme
consists
of
four
polypeptide
chains, β, β ', α and α,
and
is
designated
as ββ’α2.
In
Bacillus
subtilis
there
are
seven
polypeptide
chains ββ’ααδω1ω2 in
the
core
enzyme.
The α chain
is
present
twice.
The
sigma
factor
is
not
very
firmly
attached
to
the
core
enzyme
and
can
therefore
be
easily
isolated.
