Steady-State Studies of DNA Dynamics

Steady-state FPA experiments on DNA/ethidium complexes were undertaken by Genest et a/.(168) and Hard and Kearns 16 l72) to address a number of questions. Reliability of the results and conclusions is reduced somewhat not only by the lack of time resolution, but also by the following factors. 

The steady-state FPA of large ( 500bp) calf thymus DNA/ethidium complexes is unaffected by addition of proflavine up to one per two base pairs. From this, it is concluded that the torsion constant is unaltered(168) by intercalation of proflavine. However, in our time-resolved FPA studies of linear pBR322 DNA/ethidium complexes, the torsion constant is reduced by the factor 0.60 as proflavine is added from zero to one per two base pairs.(173) Whether this discrepancy is due to a real difference between these DNAs or 

Fluorescence microscopy techniques were also applied to study chromatin and chromosomes,(179) but those studies lie outside the scope of this chapter. 

An excellent review of tRNA structures and dynamics was presented in 1983 08°) o y subsequent fluorescence decay and FPA studies are reviewed here. The use of excitation transfer to measure intramolecular distances1 and the use of fluorescence as a probe of protein/tRNA interactions082 l85) lie outside the scope of this chapter. 

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