S1 nuclease recognizes DNA conformational junctions between left-handed helical (dT-dG n. dC-dA)n and contiguous right-handed sequences.
The ability of negative supercoiling to induce a left-handed helix in the recombinant plasmid pRW777, which contains a tract of 64 base pairs of almost perfect (dT-dG) . (dC-dA) from the mouse kappa immunoglobin gene, was studied. S1 nuclease recognizes and cleaves within the junction region which must exist adjacent to the (dT-dG)n . (dC-dA)n tract when in a left-handed state. The cleavage pattern indicates conformational flexibility and structural differences between the two existing junctions. The 64-base pair alternating copolymer undergoes the supercoil-induced formation of a left-handed state over the superhelical density range of -0.04 to -0.06, indicating that (dT-dG)n . (dC-dA) sequences form a left-handed helix less readily than (dC-dG)n . (dC-dG)n sequences of equivalent length. However, these supercoil densities are within the range found in vivo. Supercoil relaxation and antibody binding studies confirmed that the (dT-dG)n . (dC-dA)n tract in supercoiled pRW777 was in a left-handed helix.
D001483:Base Sequence; D004247:DNA; D004720:Endonucleases / Q000378:metabolism*; D009690:Nucleic Acid Conformation; D010957:Plasmids; D011089:Polydeoxyribonucleotides; D015719:Single-Strand Specific DNA and RNA Endonucleases; D013379:Substrate Specificity
D011089:Polydeoxyribonucleotides; C035586:poly(dT-dG)n.poly(dC-dA)n; D004247:DNA; D004720:Endonucleases; D015719:Single-Strand Specific DNA and RNA Endonucleases