Viral Genomes

To the tune of "Rebel Rebel" by David Bowie
Double stranded DNA
Is the only template
For direct transcription
Into mRNA
Gapped double stranded genomes
Cannot be transcribed alone
Must first be repaired by
Host cellular enzymes
More genome can be made
With action of reverse transcriptase
With single stranded DNA genomes
Either strand can initiate infection
But from a single strand of DNA
mRNA cannot be made
Doo doo doo-doo doo doo doo doo
Doo doo doo-doo doo doo doo doo
Doo doo doo-doo doo doo doo doo
Doo doo doo-doo doo doo doo doo
Every RNA virus
Encodes an RNA dependent
RNA polymerase
RdRp it is so named
The enzyme has two functions
One being genome replication
The other making mRNA
From RNA templates
In DNA viruses
Two separate enzymes are needed
The ribosome cannot access
Positive RNA in a duplex
In double stranded RNA
RdRp produces mRNA
Single stranded positive RNA
The genome can be immediately translated
But for more copies of genome to be made
There is intermediate negative RNA
Retroviruses use reverse transcriptase
To produce intermediate DNA
Into the host genome they integrate
Where host enzymes will replicate it
For single stranded negative RNA
RdRp must make
Positive RNA to be translated
And as a replication template