COMPARISON OF BASE INCLINATIONS FOR LEFT-HANDED DNA AND RNA

The Z'-form of poly (dG-m(5)dC). poly (dG-m(5)dC) in 85 % ethanol/MOPS and the Z-form poly(rG-rC). poly(rG-rC) in 4.8 M NaClO4, 20% ethanol are studied by flow linear dichroism. Simultaneous analysis of the iso tropic absorption and linear dichroism data yields the angle of inclin ation of the base normal relative to the helix axis, and the orientati on of the axis around which the bases incline. For the Z'-form of poly (dG-m(5)dC). poly(dG-m(5)dC) the inclination angles are 31.3 degrees f or guanine, and 27.9 degrees for cytosine; for the Z-form of poly(rG-r C). poly(rG-rC) they are 25.0 degrees for guanine, and 23.3 degrees fo r cytosine. The inclination angles for the Z'-form DNA are similar to those for the Z-form, and the angles for Z-form RNA are somewhat small er. The axes of inclination for guanine and cytosine are similar in al l three left-handed forms. (C) 1995 John Wiley & Sons, Inc.