Gene and genon concept: coding versus regulation

Institut Jacques Monod, Lutetia Parisorum, Île-de-France, France
Theory in Biosciences (Impact Factor: 1.23). 11/2007; 126(2-3):65-113. DOI: 10.1007/s12064-007-0012-x
Source: PubMed


We analyse here the definition of the gene in order to distinguish, on the basis of modern insight in molecular biology, what the gene is coding for, namely a specific polypeptide, and how its expression is realized and controlled. Before the coding role of the DNA was discovered, a gene was identified with a specific phenotypic trait, from Mendel through Morgan up to Benzer. Subsequently, however, molecular biologists ventured to define a gene at the level of the DNA sequence in terms of coding. As is becoming ever more evident, the relations between information stored at DNA level and functional products are very intricate, and the regulatory aspects are as important and essential as the information coding for products. This approach led, thus, to a conceptual hybrid that confused coding, regulation and functional aspects. In this essay, we develop a definition of the gene that once again starts from the functional aspect. A cellular function can be represented by a polypeptide or an RNA. In the case of the polypeptide, its biochemical identity is determined by the mRNA prior to translation, and that is where we locate the gene. The steps from specific, but possibly separated sequence fragments at DNA level to that final mRNA then can be analysed in terms of regulation. For that purpose, we coin the new term "genon". In that manner, we can clearly separate product and regulative information while keeping the fundamental relation between coding and function without the need to introduce a conceptual hybrid. In mRNA, the program regulating the expression of a gene is superimposed onto and added to the coding sequence in cis - we call it the genon. The complementary external control of a given mRNA by trans-acting factors is incorporated in its transgenon. A consequence of this definition is that, in eukaryotes, the gene is, in most cases, not yet present at DNA level. Rather, it is assembled by RNA processing, including differential splicing, from various pieces, as steered by the genon. It emerges finally as an uninterrupted nucleic acid sequence at mRNA level just prior to translation, in faithful correspondence with the amino acid sequence to be produced as a polypeptide. After translation, the genon has fulfilled its role and expires. The distinction between the protein coding information as materialised in the final polypeptide and the processing information represented by the genon allows us to set up a new information theoretic scheme. The standard sequence information determined by the genetic code expresses the relation between coding sequence and product. Backward analysis asks from which coding region in the DNA a given polypeptide originates. The (more interesting) forward analysis asks in how many polypeptides of how many different types a given DNA segment is expressed. This concerns the control of the expression process for which we have introduced the genon concept. Thus, the information theoretic analysis can capture the complementary aspects of coding and regulation, of gene and genon.

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Available from: Scherrer Klaus, Nov 12, 2015
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    • "As a result, the delimitation and definition of different types of genes is not as straightforward as it is for molecules at the lower molecular level (e.g. Gerstein et al., 2007; Scherrer and Jost, 2007a,b; Prohaska and Stadler, 2008), because it is not reasonable or practical to use overall compositional and structural identity as a criterion. This explains why the annotation and classification of genes is more difficult and controversial than the description of DNA sequence data. "
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    • "We have been glad to see that our paper (Scherrer and Jost 2007) solicited such insightful or supportive commentaries as those of Noble, of Gros, of Prohaska and Stadler, of Forsdyke, and Billeter, as well as the alternative proposal of Stadler et al., and we hope that this will trigger further conceptual discussions about the definition of the gene and inspire further research about programs of gene expression, in the light of recent advances in molecular biology and bioinformatics (Billeter 2009; Forsdyke 2009; Gros 2009; Noble 2009; Prohaska and Stadler 2008; Stadler et al. 2009). The commentaries raise some important issues. "

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