As you now know, the bacterial and archaeal RNA polyermase (RNAP) differ in complexity. Despite the fact that the cell plan of both life forms is small, relatively simple, and streamlined, the RNAPs differ remarkably in terms of complexity, where the bacterial version is built from four parts, while the archaeal version is built from 11 parts.
The non-teleological perspective would “explain” this disparity by simply informing us that there are many ways to transcribe DNA into RNA and these two RNAPs would merely reflect the many roads to Rome. At that point, we might remind people that this non-teleological perspective led biologists astray, as it prevented them from anticipating the widespread phenomena of deep homology. But worse than that, this explanation doesn’t work with these cellular RNAPs.
Consider again the interaction maps of the archaeal RNAP (left) and eukaryal RNAP (right)
What’s not shown is the map of bacterial RNAP. But it is there in both maps. In the eukaryal map, it’s just 1, 2, 3, 6 and 11 (where 3 and 11 are fused). And biochemical evidence with all three versions of the RNAP show these subunits to form the functional core. So archaebacteria and bacteria have the same RNAP, only that the archaeal version comes with added bells and whistles.
So why does the archaeal version of the RNAP have all these needless bells and whistles? I would propose that we are witnessing yet another clue that front-loading was in play. That is, the archaeal RNAP, not needed to fill bacteria-like niches, is a preadaptation to facilitate the evolution of the eukaryotic cell plan, and thus complex multicellular life. In other words, the same hypothesis that explains the existence of protein-coding introns, and explains the odd features of the signal recognition particle, also explains the unusual aspects of the archaeal RNAP.
And this front-loading hypothesis, under the guidance of PREPA, allows us to formulate a testable hypothesis – the “bells and whistles” of the archaeal RNAP – Rbp 4, 5, 7, 10, 11, and 12 – will play crucial roles in the emergence of a) the eukaryotic cell and/or b) complex, metazoan life.
Shall we now put this hypothesis to the test?