EFFECTS OF DIAMINOPURINE AND INOSINE SUBSTITUTIONS ON A-TRACT INDUCED DNA CURVATURE - IMPORTANCE OF THE 3'-A-TRACT JUNCTION

摘要

Gel migration and uranyl photoprobing have been used to study the effects of inosine and 2,6-diamino-purine (2,6-DAP) substitution on adenine-tract (A-tract) induced DNA curvature, Using a 10mer repeated sequence including five inosines we show by uranyl photoprobing that a narrow minor groove varying in phase with the helix repeat is not the cause of DNA curvature, Further, we have systematically studied by gel migration the effects on A-tract induced curvature of either single or full substitution with inosine and/or 2,6-DAP in a 5'-AAAAAGCCGC-3' sequence, DNA curvature is shown to increase when inosines are substituted for the guanosines in the sequence between the A-tracts, By comparing the effects of each monosubstitution it can be seen that when the G closest to the 3'-end of the A-tract is substituted the effect on DNA curvature is much stronger than when substitution is made at any other position, By contrast, curvature is abolished when 2,6-DAP residues are substituted for all adenines, and monosubstitution reveals that the effect of substituting a single adenine is strongest at the 3'-end of the A-tract, These results favor a model in which the curvature induced by an A-tract in DNA molecules is primarily located at the junction with the 3'-end of the A-tract, and this peculiar junction is created because the A-tract has a preference to form a non-B-DNA structure which builds up from the 5'-end.