RNA-based processes traceable to the Last Universal Common Ancestor.

<p>Universal Rfam families that show evidence of vertical inheritance (Table S1 in <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1002752#pcbi.1002752.s008" target="_blank">Text S1</a>) are all associated with the processes of translation (rRNAs, tRNAs, RNase P) and protein export (SRP RNA). A previous study examining the antiquity of protein coding genes <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1002752#pcbi.1002752-Harris1" target="_blank">[21]</a> identified only 37 universally distributed proteins which show evidence of vertical inheritance. The majority of these vertically inherited proteins are associated with translation and protein export; numbers of such proteins associated with each of the depicted processes is given in grey (original data are from Harris <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1002752#pcbi.1002752-Harris1" target="_blank">[21]</a>). The proteins associated with RNase P are not universally conserved, with archaeal and eukaryotic RNase P proteins being unrelated to their bacterial counterparts <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1002752#pcbi.1002752-Hartmann1" target="_blank">[72]</a>. While tRNA synthetases are universal, they have undergone ancient horizontal gene transfer events <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1002752#pcbi.1002752-Fournier1" target="_blank">[73]</a>, which complicates establishing the timing of their origin.</p>