Dec 7, 2023

The Virus Zoo: A Primer on Molecular Virology

Posted by in categories: biotech/medical, genetics

Genome and Structure:

HIV’s genome is a 9.7 kb linear positive-sense ssRNA.1 There is a m7G-cap (specifically the standard eukaryotic m7GpppG as added by the host’s enzymes) at the 5’ end of the genome and a poly-A tail at the 3’ end of the genome.2 The genome also has a 5’-LTR and 3’-LTR (long terminal repeats) that aid its integration into the host genome after reverse transcription, that facilitate HIV genetic regulation, and that play a variety of other important functional roles. In particular, it should be noted that the integrated 5’UTR contains the HIV promoter called U3.3,4

HIV’s genome translates three polyproteins (as well as several accessory proteins). The Gag polyprotein contains the HIV structural proteins. The Gag-Pol polyprotein contains (within its Pol component) the enzymes viral protease, reverse transcriptase, and integrase. The Gag-Pol polyprotein is produced via a −1 ribosomal frameshift at the end of Gag translation. Because of the lower efficiency of this frameshift, Gag-Pol is synthesized 20-fold less frequently than Gag.5 The frameshift’s mechanism depends upon a slippery heptanucleotide sequence UUUUUUA and a downstream RNA secondary structure called the frameshift stimulatory signal (FSS).6 This FSS controls the efficiency of the frameshift process.

Leave a reply