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Back in 1962, when I had by accident become the supervisor of Roberto Celis in Argentina, it occurred to me that antibody diversity might arise from the joining by disulphide bridges of a variety of small polypeptides in combinatorial patterns.

What attracted me to immunology was that the whole thing seemed to revolve around a very simple experiment: take two different antibody molecules and compare their primary sequences.

It's nice to be able to look at one protein, but life is driven by the interactions between proteins, so it's really essential to be able to see multiple proteins at a time to understand these interactions.

As can be seen even by this limited number of examples proteins carry out amazingly diverse functions.

The basic structure of proteins is quite simple: they are formed by hooking together in a chain discrete subunits called amino acids.

Immunologists agreed that an individual vertebrate synthesizes many millions of structurally different forms of antibody molecules even before it encounters an antigen.

A comparison between the triplets tentatively deduced by these methods with the changes in amino acid sequence produced by mutation shows a fair measure of agreement.

It is one of the more striking generalizations of biochemistry - which surprisingly is hardly ever mentioned in the biochemical textbooks - that the twenty amino acids and the four bases, are, with minor reservations, the same throughout Nature.

The immune system has evolved the capacity to react specifically with a very large number of foreign molecules with which it had no previous contact while avoiding reactivity for autologous molecules, naturally antigenic in other species or in other individuals of the same species.

It now seems certain that the amino acid sequence of any protein is determined by the sequence of bases in some region of a particular nucleic acid molecule.