5-Bromouracil

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5-Bromouracil
Chemical name	5-Bromouracil
Chemical formula	C4H3BrN2O2
Molecular mass	191.0 g/mol
CAS number	51-20-7
Disclaimer and references

5-Bromouracil (or 5-bromo-2,4(1H,3H)-pyrimidinedione or 5-BrU or 5-BU) is a component of 5-bromo-2-deoxy-uridine.

5-BrU a brominated derivative of uracil that acts as an antimetabolite or base analog, substituting for thymine in DNA and can induce DNA mutation in the same way as 2-aminopurine. It is used mainly as an experimental mutagen, but its deoxyriboside derivative (5-bromo-2-deoxy-uridine) is used to treat neoplasms.

5-BrU exists in two forms (tautomers) which both have different base pairing properties. The keto form (pictured) is complementary to adenine so this can be incorporated into DNA by aligning opposite adenine residues during DNA replication. Alternatively, the enol (or ion) form is complementary to guanine. This means that 5-BrU can be present in DNA either opposite adenine or guanine.

The two forms frequently interchange so base-pairing properties can become altered at any time. The result of this is that during a subsequent round of replication a different base is aligned opposite the 5-BrU residue. Further rounds of replication 'fix' the change by incorporating a normal nitrogen base into the complementary strand.

Thus 5-BrU induces a point mutation via base substitution. This base pair will change from a T-A to a G-C after a number of replication cycles.

[edit] References

• Griffiths, Anthony J. et al (2005). Introduction to Genetic Analysis (8th Ed.). W.H. Freeman. ISBN 0-7167-4939-4