POLYAMINE-INDUCED Z-DNA CONFORMATION IN PLASMIDS CONTAINING (DA-DC)(N)CENTER-DOT(DG-DT)(N) INSERTS AND INCREASED BINDING OF LUPUS AUTOANTIBODIES TO THE Z-DNA FORM OF PLASMIDS

Blocks of potential Z-DNA-forming (dA-dC)(n).(dG-dT)(n) sequences are ubiquitous in eukaryotic genomes. We examined whether naturally occurring polyamines, putrescine, spermidine and spermine, could provoke the Z-DNA. conformation in plasmids pDHf2 and pDHfl4 with 23 and 60 bp inserts respectively of (dA-dC)(n).(dG-dT)(n) sequences using an e.l.i.s.a. Spermidine and spermine could provoke Z-DNA conformation in these plasmids, but putrescine was ineffective. For pDHf2 and pDHf14, the concentration of spermidine at the midpoint of B-DNA to Z-DNA transition was 25 mu M, whereas that of spermine was 16 mu M. Polyamine structural specificity was evident in the ability of spermidine homologues to induce Z-DNA. Inorganic cations, Co(NH3)(6)(3+) and Ru(NH3)(6)(3+), were ineffective. Our experiments also showed increased binding of anti-DNA autoantibodies from lupus patients as well as autoimmune MRL-lpr/lpr mice to pDHf2 and pDHfl4 in the presence of polyamines. These data demonstrate that small blocks of (dA-dC)(n).(dG-dT)(n) sequences could assume the Z-DNA conformation in the presence of natural polyamines. Increased concentrations of polyamines in the sera of lupus patients might facilitate immune complex-formation involving circulating DNA and anti-ZDNA antibodies.