Induction of a tautomeric shift by 5-bromo-uracil base analogue
(a) 5-bromo-uracil
(5BU) is a modified form of thymine (T).
(b) In its keto configuration, 5BU
has the same base-pairing as T, by two H-bonds
with adenine (A). In the tautomeric enol
form, three H-bonds are available and it
pairs with the alternative purine base, guanine (G).
(c) Incorporation of 5BU into dsDNA
as a 5BU = A basepair
produces either a T = A pair from the strand with
the A, or if the 5BU
' has undergone a tautomeric shift,
a 5BU ' = G
pair from the strand with the 5BU. In the next round
of replication, the mis-incorporated G correctly pairs with a C as usual. With respect to
the original T = A basepair, the C = G
basepair is a T
C
transition mutation.
C
transition mutation. Figure © 2012 TA Brown, Introduction to Genetics (1st ed.); additional text © 2012 by Steven M. Carr