Virulent but not temperate bacteriophages display hallmarks of rapid translation initiation

Bacteriophages rely almost exclusively on host-cell machinery to produce their proteins, and their mRNAs must therefore compete with host mRNAs for valuable translational resources. In many bacterial species, highly translated mRNAs are characterized by the presence of a Shine-Dalgarno sequence motif upstream of the start codon and weak secondary structure within the start codon region. However, the general constraints and principles underlying the translation of phage mRNAs are largely unknown. Here, we show that phage mRNAs are highly enriched in strong Shine-Dalgarno sequences and have comparatively weaker secondary structures in the start codon region than host-cell mRNAs. Phage mRNAs appear statistically similar to the most highly expressed host genes in E. coli according to both features, strongly suggesting that they initiate translation at particularly high rates. Interestingly, we find that these observations are driven largely by virulent phages and that temperate phages encode mRNAs with similar start codon features to their host genes. These findings apply broadly across a wide-diversity of host-species and phage genomes. Further study of phage translational regulation--with a particular emphasis on virulent phages--may provide new strategies for engineering phage genomes and recombinant expression systems more generally.