Saturation mutagenesis of a DNA region of bend. Base steps other than ApA influence the bend.
A 60 base-pair region of a simian virus 40 DNA fragment was mutagenized to determine base-pairs that are critical for the fragment to bend. The site-directed mutagenesis saturated this region with all possible single base-pair substitutions. The mobility of each mutated fragment was measured by polyacrylamide electrophoresis at 4 degrees C and at 65 degrees C to assess the degree of bend. Four conclusions can be drawn. First, interruptions within the A tracts and changes in the phasing of the A tracts alter the degree of bend. Second, G tracts phased at a half-helical turn from an A tract are additive to the bend. Third, guanine residues in a nearest-neighbor contact with the A tracts modify the bend. Fourth, some mutations that do not obviously relate to the A tracts also alter the DNA bend and suggest clearly that base steps other than ApA are involved in sequence-directed DNA bends.
Milton
D L
DL
Department of Human Genetics, University of Utah, Salt Lake City 84132.
Casper
M L
ML
Gesteland
R F
RF
D001482:Base Composition; D001483:Base Sequence; D002213:Capsid / Q000235:genetics; D004279:DNA, Viral / Q000235:genetics; D004591:Electrophoresis, Polyacrylamide Gel; D008969:Molecular Sequence Data; D009154:Mutation; D009690:Nucleic Acid Conformation; D010957:Plasmids; D013539:Simian virus 40 / Q000235:genetics*
D004279:DNA, Viral