RNA secondary structure of the feline immunodeficiency virus 5'UTR and Gag coding region

The 5' untranslated region (5'UTR) of lentiviral genomic RNA is highly structured, and is the site of multiple RNA-RNA and RNA-protein interactions throughout the viral life cycle. The 5'UTR plays a critical role during transcription, translational regulation, genome dimerization, reverse transcription priming and encapsidation. The 5'UTR structures of human lentiviruses have been extensively studied, yet the respective role and conformation of each domain is still controversial. To gain insight into the structure-function relationship of lentiviral 5'UTRs, we modelled the RNA structure of the feline immunodeficiency virus (FIV), a virus that is evolutionarily distant from the primate viruses. Through combined chemical and enzymatic structure probing and a thorough phylogenetic study, we establish a model for the secondary structure of the 5'UTR and Gag coding region. This work highlights properties common to all lentiviruses, like the primer binding site structure and the presence of a stable stem-loop at the 5' extremity. We find that FIV has also evolved specific features, including a long stem loop overlapping the end of the 5'UTR and the beginning of the coding region. In addition, we observed footprints of Gag protein on each side of the initiation codon, this sheds light on the role of the sequences required for encapsidation.