Specific residues within the predicted coiled-coil motif are required for dimerization and RNA binding. Representation of MBP-Rev constructs evaluated for dimerization and RNA binding. Rev165 is the reference construct used for all comparisons; Rev135 contains a 30 aa deletion of the non-essential exon1 region, and Rev145-165 contains only the 21 C-terminal amino acid residues of Rev. Indicated mutations in ARM-1, ARM-2 and the coiled-coil (C-C) motif were introduced into Rev135. Nuclear export activity of Rev cDNAs containing each mutation measured in a previous study is indicated , nd: not determined. B. Oligomeric forms of purified MBP-Rev proteins. The purified MBP-Rev proteins were analyzed by Coomassie-stained Blue-native PAGE in the presence of 0.2% SDS. The L95D mutation in the predicted interhelical interface abolishes dimerization whereas mutation of residues flanking L95 (AALA) does not affect dimerization. Mutation of ARM-1 (AADAA) and or ARM-2 (KAAAK) does not affect dimerization. C. RNA-binding activity as measured by UV cross-linking and SDS-PAGE (reproduced from ). The L95D mutation in the predicted coiled-coil interhelical interface causes a dramatic decrease in RNA binding, whereas mutation of residues flanking L95 (AALA mutant) does not affect RNA binding. Marked reduction of RNA binding activity was also observed in ARM-1 and ARM-2 mutants (AADAA and KAAAK, respectively).