Positive (+) single-strand (+ssRNA)

Definition

Positive single-strand RNA (+ssRNA) viruses have genomes that can directly serve as mRNA for protein synthesis. They are immediately infectious upon entering a host cell.

5 Must Know Facts For Your Next Test

1. +ssRNA viruses replicate in the cytoplasm of the host cell.
2. The genome of +ssRNA viruses can be directly translated by host ribosomes.
3. Examples of +ssRNA viruses include the common cold (rhinovirus) and COVID-19 (SARS-CoV-2).
4. +ssRNA viruses often use their RNA-dependent RNA polymerase to replicate their genome.
5. The viral life cycle of +ssRNA viruses includes attachment, entry, translation, replication, assembly, and release.

Review Questions

• What is the primary function of the +ssRNA genome once it enters a host cell?
• Name two examples of diseases caused by +ssRNA viruses.
• Where does replication of +ssRNA viruses primarily occur within the host cell?

Related terms

Negative single-strand RNA (-ssRNA): -ssRNA must be transcribed into a complementary positive strand before translation.

Reverse Transcriptase:

An enzyme used by retroviruses to convert their RNA into DNA.

Capsid:

The protein shell that encases the viral genome.