Unusual conformation of (dA)n·(dT)n-tracts as revealed by cyclobutane thymine – thymine dimer formation

摘要

Cyclobutane dimer formation has been used to probe conformation of (dA)_n·(dT)_n-tracts cloned in plasmid DNA. The observed dimer probability patterns for (dA)_n·(dT)_n -tracts with n ≥ 4 exhibit maximum intensity at the 3′-terminal TT site of T_n-tract, whereas photoreactivity at all the other TT sites is inhibited. Both temperature and dimethyl sulfoxide increase dimer formation within T_n-tracts and result in an even dimer pattern. The data obtained have been interpreted in terms of an unusual structure adopted by (dA)_n·(dT)_n -tracts. An influence of flanking base pairs, ethidium bromide binding and ionic strength has also been studied.