Deletions near the N-terminus of HIV-1 Rev reduce RNA binding affinity anddominantly interfere with Rev function irrespective of the RNA target

The contributions of the near N-terminal residues of Rev protein of HIV wer e investigated by analyzing N-terminal deletions of Rev in the context of a Rev/MS-C fusion protein that can bind and activate both the Rev responsive element (RRE) and the MS2 phage translational operator RNAs. Rev/MS-C fusi on proteins deleted for residues 3-19 of Rev retained trans-activation pote ntial for both RRE and MS2 targets. Coincidentally, peptides spanning resid ues 17-87 or 22-85 were functionally competent for trans-activation of RRE containing HIV-1 gag mRNA. Deletion of residues 18-24 of Rev in the Rev/MS- C fusion protein abolished the activation potential for both RRE and MS2 ta rgets, although this mutant was competent for specific RNA binding, protein multimerization, and nuclear and nucleolar localization. Four mutants domi nantly interfering with Rev activation of RRE were mapped near the N-termin us of Rev; (i) between residues 18 and 24, (ii) 25-34, (iii) 43-50, and (iv ) 51-60. Of these, the mutant lacking residues 18-24 was a novel trans-domi nant inhibitor of Rev and Rev/MS-C for activation of RRE or MS2 RNA, while the oligomerization domain mutants mapping between residues 25-34 or 51-60 inhibited the activation of RRE rather than MS2 RNA.