STRUCTURAL REDESIGN AND STABILIZATION OF THE OVERLAPPING TANDEM BETA-TURNS OF RNA-POLYMERASE-II

Peptides representing single repeat units of the carboxy-terminal doma in (CTD) of RNA polymerase II (Tyr-Ser-Pro-Thr-Ser-Pro-Ser-Tyr-NH2, 1) contain overlapping Ser-Pro-Xaa-Xaa beta-turn forming sites which per mit their overall structure to closely resemble members of the quinoxa line class of antitumor DNA bisintercalators. We have modified this na tive sequence at the i+2 positions of each beta-turn unit by substitut ing Gly or D-Ala in an attempt to preorganize this structure in aqueou s solution. CD and NMR spectroscopic investigations confirmed the pres ence of type II beta-turns within each of the substituted peptides in contrast to the native sequence which contains a relatively low popula tion of turn structure. In addition, an examination of singly substitu ted peptides suggests that an increase in the population of p-turn str ucture within the amino-terminal Ser-Pro-Xaa-Xaa site also increased t he formation of beta-turn structure in the carboxy-terminal (unmodifie d) Ser-Pro-Xaa-Xaa site; in comparison, substitution in the carboxy-te rminal site did not influence structure in the remaining portion of th e peptide. Overall, these results suggest that the structures formed c ould provide unique, preorganized linkers for the construction of nove l DNA-interactive bisintercalators. (C) Munksgaard 1996.