Long-range translational coupling in single-stranded RNA bacteriophages: an evolutionary analysis

Abstract

In coliphage MS2 RNA a long-distance interaction (LDI) between an internal segment of the upstream coat gene and the start region of the replicase gene prevents initiation of replicase synthesis in the absence of coat gene translation. Elongating ribosomes break up the repressor LDI and thus activate the hidden initiation site. Expression studies on partial MS2 cDNA clones identified base pairing between 1427-1433 and 1738-1744, the so-called Min Jou (MJ) interaction, as the molecular basis for the long-range coupling mechanism. Here, we examine the biological significance of this interaction for the control of replicase gene translation. The LDI was disrupted by mutations in the 3'-side and the evolutionary adaptation was monitored upon phage passaging. Two categories of pseudorevertants emerged. The first type had restored the MJ interaction but not necessarily the native sequence. The pseudorevertants of the second type acquired a compensatory substitution some 80 nt downstream of the MJ interaction that stabilizes an adjacent LDI. In one examined case we confirmed that the second site mutations had restored coat-replicase translational coupling. Our results show the importance of translational control for fitness of the phage. They also reveal that the structure that buries the replicase start extends to structure elements bordering the MJ interaction.

Bacteriophage T4 Genome

“…In compact, densely coding phage genomes, translationally coupled gene arrangements are commonplace, although few have been explicitly studied. Translational coupling has been examined in RNA phages (638) and ssDNA Ff phage (1230). The very first intimations of translational coupling in T4 were observed by Stahl et al (1035).…”

Recent insights on RNA folding mechanisms from catalytic RNA

“…In some examples, refolding of the mRNA is coupled to translational control of downstream genes by disrupting RNA structures that inhibit translational initiation [127,128]. A particularly clear example of this idea comes from work on the group I intron from the thymidylate synthase (td) gene of bacteriophage T4.…”

Translational Control of Viral Gene Expression in Eukaryotes

“…Where appropriate, we have focused on specific virus systems to present examples of the diverse mechanisms by which viruses overcome the problems of translational dependence. For complementary material on mRNA translation, virus-host interactions, host antiviral pathways, and the virus-host interactions of lower eukaryotes and bacteria, we direct the reader to several fine texts and reviews (1,10,117,137,179,199,303,324,353,415,416,428,455,480,484). We begin this review with a brief overview of the current models for eukaryotic mRNA translation, including points of translational control, and effects on host translation due to virus infection.…”