Bromine Activation of Thymine, Guanine, and Cytosine

Optimal bromination of a DNA probe is in the range 30—35 bases per 1000 bases, a level that can be controlled by the amount of N-bromosuccinimide added. Overlabeling can prevent specific interactions with target DNA, even if the point of initial modification is not a hydrogen bonding site. 

Hgure 397 Reaction of guanine bases with N-biomosuccinimide causes bromination at the C-8 position of the ring. Amine nucleophiles can be coupled to this active derivative by nucleophilic displacement. Reaction of diamine compounds results in amine terminal spacers that can be further modified to contain detectable components. 

The major disadvantage with bromination is the extreme toxicity of bromine. Use a fume hood for all operations. Avoid the breathing of fumes or contact with skin or eyes. Protective clothing and gloves are recommended. 

Protocol for Labeling Nucleic Acids by N-Bromosuccinimide Activation 

In a fume hood, dissolve N-bromosuccinimide (Sigma) in water at a concentration of 1.42 mg/ml. 

Conjugation via Bromine Activation of Thymine, Guanine, and Cytosine 

The nucleotide bases of DNA and RNA can be activated with bromine to produce reactive intermediates capable of coupling to nucleophiles (Traincard et al., 1983 Sakamoto et al., 

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