Do Viruses Exchange Genes across Superkingdoms of Life?

Malik, Shahana S.; Azem-e-Zahra, Syeda; Kim, Kyung Mo; Caetano-Anollés, Gustavo; Nasir, Arshan

Two factors were considered when postulating the direction of gene transfer (Figure 1) : (i) the reported biochemical function of an FSF (e.g., virion synthesis or ATP synthesis), and (ii) spread of that FSF in the proteomes of cellular superkingdom(s). For example, if an FSF involved in capsid assembly (a virus hallmark function) was detected in only few cellular proteomes (e.g., <1%), then this FSF was determined to have transferred horizontally from virus-to-cell. In turn, if an FSF involved in cellular hallmark function (e.g., metabolism) and widespread in cellular proteomes (e.g., >60% presence) was detected in some viral proteomes then this was FSF was determined to have transferred horizontally from cell to viruses. The exception would be the presence of "cell-like" FSFs in the proteomes of all three virus groups, i.e., archaeoviruses, bacterioviruses, and eukaryoviruses, suggesting a cellular co-existence between viral and cellular ancestors prior to diversification of modern life (Nasir et al., 2012a,b) . Thus, both the FSF spread and its biochemical function were considered when postulating the direction of gene transfer.