Single Stranded RNA viruses

RNA viruses can be single or double stranded.


The single stranded virus can be of three types:


Positive strand ssRNA:  It can also be called as ‘same sense to viral mRNA.’ It can be immediately translated into proteins; transcription is not required. In other words, the viral strand is “same-sense“. Its genetic code is equivalent the coding strand (which is generally the 5′ to 3′ strand in double-stranded genomes).

Negative strand ssRNA: They are antisense to viral mRNA. These are first copied to positive strand ssRNA; which is further translated.

The important point is that there is no DNA in the life cycle of the above two types of viruses at all. RNA-dependent RNA polymerase is used for the replication of the above two.


Another type of ssRNA virus is there, known as the ssRNA-RT virus. The virus has a positive strand. This virus has a DNA intermediate in the life cycle. Reverse transcriptase enzyme first converts RNA into DNA; then this DNA is used for replication of the genome.