Making Many Proteins from a Compact Genome | AI Learning Guide

Think about the problem: a viral genome is tiny, but the virus needs many proteins. One solution is to translate the whole genome as a single long polyprotein, then cut it into individual proteins with proteases. This is common in positive-sense RNA viruses. The timing of the cuts can control when each protein becomes active. Another solution is ribosomal frameshifting. Here the ribosome hits a specific RNA sequence and slips by one nucleotide, changing the reading frame. That produces a different protein from the same RNA. HIV-1 uses this to make the Gag-Pol polyprotein, which includes reverse transcriptase and integrase. Both strategies let a small genome encode a complex set of proteins.

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Polyprotein processing

A single long polypeptide is translated from one open reading frame and then cleaved by proteases into individual proteins. This is common in positive-sense RNA viruses such as picornaviruses and flaviviruses. The timing of cleavage can regulate when each protein becomes active.

Ribosomal frameshifting

A specific RNA structure causes the ribosome to shift reading frame, producing a different protein from the same RNA. HIV-1 uses this to make the Gag-Pol polyprotein, which includes reverse transcriptase and integrase. This increases coding capacity without increasing genome size.

Two strategies for compact genomes

Polyprotein processing

One long polypeptide translated
Cleaved by proteases into functional proteins
Common in positive-sense RNA viruses
Allows temporal regulation of protein activity

Ribosomal frameshifting

Ribosome shifts reading frame at a specific sequence
Produces a different protein from the same RNA
Used by HIV-1 to make Gag-Pol
Increases coding capacity without larger genome