Further speculations on the minimal genome

Obviously, only speculations can help at this point. One way to speculate is to imagine a kind of theoretical knock down of the genome, reducing cellular complexity and at the same time part of the non-essential functionality (Luisi et ah, 2002). 

Thanks to the outside supply of substrates, such a cell should be capable of selfmaintenance and of self-reproduction, including replication of the membrane s components. However it would not make low-molecular-weight compounds and would not have redundancies for its own defense and security - all self-repair mechanisms are missing. Also, there is the problem of leakage and lack of concentration gradients and cell division would be simply due to a physically based statistical process. 

There is of course no proof that this theoretical constmct would work - and this also holds of course for Moya s 206 genes. It is nevertheless instmctive to go further with these theoretical knock down experiments. 

The next victims would be ribosomal proteins. Can we take them out There are some indications that ribosomal proteins may not be essential for protein synthesis (Zhang and Cech, 1998), and there are other suggestions about an ancient and simpler translation system (Nissen et al., 2000 Calderone and Liu, 2004). If we accept this, and take out the 55 genes of the ribosomal proteins and some other enzymes, around 110 genes (second column of Table 11.4) would be obtained. 

A large portion of the above mentioned genes correspond to RNA and DNA polymerases. A number of data (Suttle and Ravel, 1974 Lazcano et al, 1988 1992 Frick and Richardson, 2001) suggest that a simplified replicating enzymatic repertoire - as well as a simplified version of protein synthesis - might be possible. From all this, the idea that a single polymerase could play multiple roles as a DNA polymerase, a transcriptase, and a primase, is conceivable in the very early cells (Luisi et al., 2002). 

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Further speculations on the minimal genome Table 11.3. Core of a minimal bacterial gene set ... 

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