Spectroscopic evidence of a DNA bend in solution is presented by analy
zing model 15-mer duplexes spin-labeled with the five-atom-tethered ni
troxide DUAP located in the major groove. Three 15-mers containing AAT
T with DUAP enzymatically incorporated into three different positions
yielded nearly identical line shapes while a fourth 15-mer containing
AAATT produced an EPR spectrum with significant additional line broade
ning. These results are interpreted according to the dynamic cylinder
model where the DNA dynamics are decoupled into overall and internal c
ontributions. It is shown that the AAATT sequence induces a change in
the internal dynamics characterized by local ordering of DUAP. The inc
rease in ordering evident in 15-mers containing AAATT rather than AATT
suggests that the former sequence gives rise to a bend toward the maj
or groove resulting in spatial restriction of the probe.