Probing the structure of RecA–DNA filaments. Advantages of a fluorescent guanine analog

The RecA protein of Escherichia coli plays a crucial role in DNA recombination and repair, as well as various aspects of bacterial pathogenicity. The formation of a RecA–ATP–ssDNA complex initiates all RecA activities and yet a complete structural and mechanistic description of this filament has remained elusive. An analysis of RecA–DNA interactions was performed using fluorescently labeled oligonucleotides. A direct comparison was made between fluorescein and several fluorescent nucleosides. The fluorescent guanine analog 6-methylisoxanthopterin (6MI) demonstrated significant advantages over the other fluorophores and represents an important new tool for characterizing RecA–DNA interactions.