Figure 3

Heterodimer complementation. Because it is a symmetric dimer, every coat protein molecule contains two RNA-binding sites, each related to the other by a dyad axis. An individual RNA-binding site is in turn comprised of two half-sites, A and B (or A' and B'), where a half-site is defined by the contribution of an individual submit of the dimer to one intact binding site. An "x" indicates the introduction of a mutation into either half-site A (and A') or B (and B'). In mutant homodimers both binding sites are inactive and a translational repressor defect results. However, when heterodimers are produced from coat proteins having lesions in different half-sites, one intact binding site is created and translational repressor function is restored. We call this heterodimer complementation.