Terminal transferase buffer

5x terminal transferase (or tailing) buffer may be prepared according to the following method:

1. Equilibrate 5 g of Chelex 100 (Bio-Rad) with 10 ml of 3 M potassium acetate at room temperature.

2. After five minutes, remove excess liquid by vacuum suction. Wash the Chelex three times with 10 ml of deionized H₂0.

3. Prepare a 1 M solution of potassium cacodylate. Equilibrate the cacodylate solution with the treated Chelex resin.

4. Recover the cacodylate solution by passing it through a Buchner funnel fitted with Whatman No. 1 filter paper.

5. To the recovered cacodylate add in order: H₂0, dithiothreitol, and cobalt chloride to make the final concentrations of 500 mM potassium cacodylate, 1 mM dithiothreitol, and 20 mM CoCl₂.

Store the buffer in aliquots at -20°C.