The Role of tRNAs in Cyanophages

Cyanophages, viruses infecting cyanobacteria, play key roles in the life cycle, biodiversity, evolution, and ecological modulations of their hosts. Accumulating evidence that a variety of photosynthesis-related and other host-like genes are found in genomes of cyanophages underscores the close relationship cyanophages have with the gene pools of their hosts during the infection cycle. An hypothesis follows that cyanophages are excellent mediators and innovators in lateral gene transfer and gene birth events. Cyanophages of the Myoviridae family appear to incorporate full-length tRNA genes into their genomes apart from host-like genes. We evaluated the possible effect of those tRNAs on the expression of cyanophages and cyanobacterial genes using the tRNA Adaptation Index, which measures the extent a given pool of tRNAs affects the translation of genes taking into account their codon usage (dos Reis, Savva et al., 2004). We show that, using the self-born tRNAs, myoviruses can efficiently harness the translation machinery of their hosts while maintaining genomes with considerabley lower GC-contents. In particular, the myoviral psbA and psbD genes, encoding for the D1 and D2 core proteins of the photosystem II, respectively, are seen to be better adapted to the addition of the viral tRNAs, when compared with their cyanobacterial counterparts from which they originated.