Abstract
Isomerization of a closed to open complex of a promoter upon
RNA polymerase binding involves base unpairing at the −10 region.
After potassium permanganate sensitivity of unpaired thymine residues,
we studied base unpairing at the −10 region during isomerization upon
RNA polymerase binding at the
P1
and
P3
promoters of the
gal
operon. Substitution of adenine by
2-amino purine (2-AP) at the invariable A⋅T base pair at the −11
position of
P1
and
P3
prevented unpairing
not only at that position but also at the other downstream positions,
suggesting a “master” role of the adenine base at −11 of the
template strand in overall base unpairing. 2-AP at −11 did not inhibit
the formation of RNA polymerase⋅promoter complex and subsequent
isomerization of the polymerase. Substitution of adenine by 2-AP at
several other positions did not affect thymine unpairing. Changing the
position of the amino group from C6 in adenine to C2 in 2-AP is
mutational only at the master switch position, −11.
