The central dogma, enunciated by Crick in 1958 and the keystone of molecular biology ever since, is li kely to prove a considerable.over-simplification."
THIS quotation is taken from the beginning of an unsigned article1 headed "Central dogma reversed", recounting the very important work of Dr Howard Temin1 and others' showing that an RNA tumour virus can use viral RNA as a template for DNA synthesis. This is not the first time that the idea. of the central .dogma. has been mis understood, in one way or another. In this article I explain why the term was originally introduced, its true meaning, and state why I think that, properly under stood, it is still an ides. of fundamental importance.
The central dogma was put forward4 at a period when. much of what we now know in molecular genetics was not established. All we had to work on were certain frag mentary experimental results, themselves often rather uncertain and confused, and a bq_uudless optimjsm that the basic concepts involved were rather simple and
}JNbably much the same in all living things. In such a. situation well constructed theories can play a really useful
part in stating problems clearly and thus guid ing experi
ment.
The two central concepts which had been produced,
originally without any e>.-.plicit statement of the simpli.fica.
tion being introduced, were those of sequential information
and of defined alphabets. Neither of these steps was
trivial. Because it was abundantly clear by that time
that a protein had a well defined three dimensional struc
ture, and that its activity depended crucially on tills
structure, it was necessary to put the folding-up process
on one side, and postulate that, by and large, the poly
peptide chain folded itself up. Trus temporarily reduced the central problem from a three dimensional one to a one dimensional one. It was also necessary to argue that in spite of the miscellaneous list of amino-acids found in proteins (as then given in all biochemical text• books) some of them, such as phosphoserine, were second ary modifications; and that there was probably a. univArsa1 set of twenty used tlu•oughout nature. In the same way minor modifications to the nucleic acid bases were ignored; uracil in RNA was con.