Stream of Codes

Most of the papers which have been published on biological codes do not make any reference to their definition. This is the case, for example, of the reports which have described and discussed a truly remarkable wealth of experimental data on the Adhesive Code (Readies and Takeichi, 1996; Shapiro and Colman, 1999), on the Sugar Code (Gabius, 2000; Gabius et al., 2002), and on the Histone Code (Strahl and Allis, 2000; Jenuwein and Allis, 2001; Turner, 2000; 2002; Gamble and Freedman, 2002; Richards and Elgin, 2002).

The practice of studying something without precisely defining it is fairly common in many sciences, and biology is no exception. The paradigmatic example is life itself, a phenomenon that we keep studying even if nobody seems to agree on its definition. Another instructive case is the concept of species, for which there is no definition that is universally valid and yet this does not prevent biologists from doing experiments, obtaining results and making sensible predictions on countless species of living creatures. Precise definitions, in short, are not always essential, but in some cases they are, and this is one of them. More precisely, we should be aware that an operative definition of organic codes in terms of adaptors would have provided a crucial guideline in at least two important cases:

1. One is the research on new biological codes such as the Adhesive Code, the Sugar Code, and the Histone Code. The problem here is that the experimental data suggest the existence of organic codes but do not prove it. And yet the results could have been conclusive because they are all compatible with the existence of true adaptors. On the face of the evidence, for example, it is most likely that lectins are the adaptors of the Sugar Code and that cadherins are the adaptors of the Adhesive Code. If that had been proved, there would be no doubt that we are in the presence of true organic codes. But people did not use a definition of codes based on adaptors, so they did not look for adaptors.

2. The second case is that of the classical research on signal transduction. Here the amount of experimental data is so enormous to be beyond description, and yet there is a remarkable paradox in this field. The only logical explanation of the facts is that signal transduction is based on organic codes and yet the word "code" has never been mentioned, so people have never looked for coding rules. The evidence has actually proved that signal transducers have the experimental characteristics of true adaptors, and yet the word "adaptors" has never been mentioned with reference to a code. This habit could well go on indefinitely by inertia, and only a precise definition of organic codes can convince people that an alternative (and much more convincing) explanation of the facts already exists.

It has been the existence of adaptors which has proved the reality of the Genetic Code, and the same is going to be true for the Signal Transduction Codes, for the Adhesive Code, for the Sugar Code, and for the Histone Code. An operative definition based on adaptors, furthermore, is the only scientific instrument that can allow us to prove the existence of other organic codes in Nature. And when we really start looking for them, we may well discover that so far we have only scratched the surface. That there is a long golden stream of organic codes out there.

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