Why Do Retroviruses Package Dimeric gRNAs?
The fact that all other viruses encapsidate single copy genomes begs the question of why retroviruses co-package two gRNAs. One reason may be economy of scale: RNA dimerization allows formation of a unique structure—the dimer linkage—that distinguishes gRNAs from mRNAs. Monomeric HIV-1 RNAs are packaged when engineered with tandem dimer linkages, underscoring the importance of this RNA structure, and not gRNA counting per se, to packaging [24]. Co-packaging gRNAs allows retroviruses to generate intact proviruses despite pervasive gRNA nicking [4] (Figure 1E). Template switching during reverse transcription is probably why retroviruses maintain infectivity when their gRNAs are damaged by gamma rays, and why retroviruses are much less radiation-sensitive than RNA viruses like vescicular stomatitis virus [25]. Researchers previously thought retroviral recombination might be mutagenic, but these notions have been dispelled [4]. HIV-1 particles with two gRNAs generate full-length proviruses
