S1-NUCLEASE RECOGNIZES DNA CONFORMATIONAL JUNCTIONS BETWEEN LEFT-HANDED HELICAL (DT-DG)N.(DC-DA)N AND CONTIGUOUS RIGHT-HANDED SEQUENCES

  • 1 January 1984
    • journal article
    • research article
    • Vol. 259  (3) , 1963-1967
Abstract
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).cntdot.(dC-dA) from the mouse .kappa. Ig gene, was studied. S1 nuclease recognizes and cleaves within the junction region which must exist adjacent to the (dT-dG)n.cntdot.(dC-dA)n tract when in a left-handed state. The cleavage pattern indicates conformational flexibility and structural differences between the 2 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.cntdot.(dC-dA) sequences form a left-handed helix less readily than (dC-dG)n.cntdot.(dC-dG)n sequences of equivalent length. These supercoil densities are within the range found in vivo. Supercoil relaxation and antibody binding studies confirmed that the (dT-dG)n.cntdot.(dC-dA)n tract in supercoiled pRW777 was in a left-handed helix.