Question

Simple retrovirus encodes three essential genes. Draw a diagram that depicts an integrated provirus with these three genes in the correct order. Show that the first two genes are out of frame relative to each other. Make sure to label the three genes and indicate the correct position of the long terminal repeats. When one considers the general rule that eukaryotic cells use mononcistronic mRNAs, explain how the pol and env proteins are produced from the provirus.

Answer 1

Three essential genes of simple retrovirus are the gag, pol and env.

gag encodes group specific antigen, proteolytic cleavage of Gag precursor generates three core structural proteins.

pol is responsible for reverse transcription, protease activity and integration into the host. The proteolytic cleavage of Pol precursor also generates three viral enzymes; reverse transcriptase, integrase and protease.

env encodes envelop glycoprotein

Simple retroviruses produce only two mRNAs: the full-length viral RNA which acts as the mRNA for gag and gag–pol and the sub-genomic mRNA that encodes the env gene.