Questions for the origin of life: why RNA, why four?

23 Oct 2009

Friday 23 October 2009

Speaker: Professor David Penny, Theoretical Biologist, Alan Wilson Centre for Molecular Ecology and Evolution, Massey University, Palmerston North, New Zealand

Venue: Bio21 Institute Auditorium, 30 Flemington Road, Parkville 

Time: 1.00 to 2.00pm

No RSVP Required. All welcome.

Enquiries: Pamela Morison  Pamela.Morison@rch.org.au or Sri Ramarathinam srihr@unimelb.edu.au

Lecture outline:
The RNA-world hypothesis is that RNA predated both proteins and DNA during the origin of life. We must ask whether there is something special about RNA - or about life itself. By taking living systems down to 2K and back, after which they recover and reproduce, supports the concept that life is a natural property of matter. But are there equally good alternatives to modern metabolism and to RNA; was it just chance that RNA occurred first? Ribose (and later deoxyribose) does allow complementary self replication by some nucleotides, but the standard AUCG genetic alphabet is not the only possible alphabet. Is the current RNA alphabet optimal? We use computational tools to infer the RNA secondary structure (shape) from a given RNA sequence. Statistics from RNA shapes are gathered with respect to alphabet size and then simulations based upon the replication and selection of fixed sized RNA populations are used to investigate the effect of alternative alphabets upon RNA's ability to step through a fitness landscape. These results show that for low copy fidelity the canonical (4-letter) alphabet is fitter than two, six- and eight-letter alphabets. In higher copy-fidelity experiments, six-letter alphabets outperform the four-letter alphabets, suggesting that the canonical alphabet is not a global optimum and is indeed a relic of the RNA world. The step from RNA to encoded protein synthesis is still the hardest step to envisage and to test experimentally. Conceptual progress is possible if we assume that the current ribosome (used for making proteins) was initially an RNA replicase that added three nucleotides at a time (a ‘triplicase'). This would solve the current ‘processivity' problem of RNA-based RNA replicases whilst still retaining the fundamental scientific principle of continuity.

This lecture is a more technical adjunct to the free lecture Origin of life: from Darwin to the metabolome of primordial soup (followed by Q&A and panel discussion) by Prof Penny.

Date & time: Thursday 22 October at 6.00 to 8.00pm.

Venue: Sunderland Lecture Theatre, Ground Floor, Medical Building corner of Grattan Street & Royal Parade, The University of Melbourne (use main entry opposite Berkeley St)

 Read more about the lecture.