SPECTROSCOPIC STUDIES ON ACETYLAMINOFLUORENE-MODIFIED (DT-DG)N.(DC-DA)N SUGGEST A LEFT-HANDED CONFORMATION

  • 1 January 1982
    • journal article
    • research article
    • Vol. 257  (17) , 166-171
Abstract
CD [circular dichroism] spectroscopy on the double-stranded strictly alternating dinucleotide polymer (dT-dG)n.cntdot.(dC-dA)n partially modified by N-acetoxy-N-acetyl-2-aminofluorene suggests a left-handed conformation in concentrated NaCl solutions. Modification of the (dT-dG)n.cntdot.(dC-dA)n polymer with acetylaminofluorene is required to promote formation of the left-handed helix since high salt concentrations and several other ionic conditions, which cause a similar transition for (dG-dC)n.cntdot.(dG-dC)n, are ineffective. Substitution of dC with 5-methyl dC in (dT-dG)n.cntdot.(dC-dA)n does not facilitate formation of a left-handed helix, also in contrast to results found for (dG-dC)n.cntdot.(dG-dC)n. A 62-base pair tract of almost perfectly alternating (dT-dG)n.cntdot.(dC-dA)n from the 3''-side of the mouse .kappa. Ig gene modified with acetylaminofluorene undergoes the salt-induced transition to a left-handed helix when studied within a 140-base pair restriction fragment. High NaCl concentrations alone will not cause the transition for this 62-base pair tract in this fragment nor in the recombinant plasmid pRW777, which contains this fragment.