Chapter 27, Problem 1CHI

No temperate RNA phages have yet been discovered. How might this absence be explained?

Summary Introduction

The term temperate indicates the ability of a bacteriophage that shows a lysogenic life cycle. Most of the temperate phages but not all the phages are able to integrate its genome into the genome of the host, becoming a prophage. A temperate phage possesses the ability to undergo lytic life cycle and produces phage progeny.

Explanation of Solution

Retroviruses possess positive-strand RNA genomes. Yet, their genome does not work like mRNA. Instead, the single-stranded RNA (ssRNA) is first converted into double-stranded DNA (dsDNA) by the retroviruses with the help of enzyme reverse transcriptase, a multifunctional enzyme. The dsDNA then incorporates itself into the DNA of the host, where it can be function as a template for the synthesis of mRNA as well as the synthesis of plus-strand RNA genome.

A copy of their genome is integrated into the bacterial chromosome (prophage DNA) or an extrachromosomal element is maintained by the temperate phages. A bacteriophage that contains the RNA genome would need reverse transcriptase to produce a dsDNA replica to become lysogenic.