RpoB is involved in translating DNA into RNA. Both, like the genes for ribosomalRNA, are old and ubiquitous.
ECONOMIST: A new domain of life
2.
After a false start pursuing what are known as ribosomalRNA genes which are involved in protein synthesis and are believed by some people to be the genetic core around which the rest of life accreted he lighted on two genes called RecA and RpoB.