User:Federico Castro M/Projects/VSFH

This project is about designing an organism that resembles the Last Universal Common Ancestor and whose construction is feasible.

Replication machinery

We have to start by:

• Estimate the genomic size of LUCA.

Concivably an organism could survive in a controlled environment with a minimal genome of just 113kbp and 151 genes (Forster 2006). However, recent estimates sugest that LUCA was complex and probably had more than 600 genes (Kooning 2003).

• Check if a RNA genome can sustain such genome size.

RNA is much more error-prone than DNA due to its higher mutation rate, so that RNA molecules cannot exceed certain size (Eigen limit) without falling into replicative catastrophe (Eigen 2002). This limit is small ~30-50kb which is only enough for a dozen genes or so.

Moreover, the largest viral RNA genomes identified so far does not exceed 30kb. It is reasonable to assume that the largest modern RNA viruses are indicative of the upper size limit for an RNA world genome.

• Did LUCA have the necesary genetic machinery to support DNA?

The findings of three conserved genes that were associated with transcription and replication of DNA (Harris 2002) sugest that it did have DNA machinery.

The idea of a LUCA that had and maintained DNA has been supported by David Penny and Anthony Poole (Penny & Poole, 1999) argumenting that an eukaryotic genetic machinery is, actually, and ancestral characteristic.

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