Genetic Analysis 291culminated with the Central Dogma was that genes are repositories of protein-
coding sequences. Canonical genes code for proteins.
No great wonder, then, that many biologists (and journalists) have
taken the central dogma to imply that, with very few exceptions, a
DNA sequence qualifies as a gene only if it can produce a protein.
[Gibbs, 2003, 47]Crick was careful to state an explicit reservation, “not necessarily directly”,
when asserting that “the main function of the genetic material is to control the
synthesis of proteins”. However, the dogmatic role that the Central Dogma ful-
filled was to uphold an extreme reductionist conception (see, e.g., Judson [1979,
333–340]), according to which “what holds forE. coliholds for the elephant” —
a dictum related by some to Crick by others to Monod — could not be main-
tained any more when molecular geneticists turned their attention to eukaryotes.
A persistent problem was the fact that the amount of DNA per cell in eukary-
ote cells was orders of magnitude greater than that of prokaryotes. Considering
that constructing and maintaining cells involves largely household functions, most
probably common to eukaryotes and prokaryotes alike, this presented a paradox.
Together with his asserting the Central Dogma, Crick also formulated the the-
oretical framework based on the experimental evidence, for its materialization.
“From many points of view it seems highly likely that thepresence of RNA is
essential for the cytoplasmic protein synthesis” [Crick, 1958, 150]. He predicted
this molecule, later known as the messenger-RNA, to be transcribed on the DNA.
“Both DNA and RNA have been shown to carry some of the specificity of protein
synthesis” [Crick, 1958,151]. He further formulated the adaptor hypothesis,
It is therefore a natural hypothesis that the amino acid is carried to the
template by an ‘adaptor’ molecule, and that the adaptor is the part
which actually fits on the RNA. In its simplest form one would require
twenty adaptors, one for each amino acid. [Crick, 1958, 155]These adaptor molecules, or transfer-RNAs, were shown to be involved in the
translation of the nucleotide sequence code into an amino-acid sequence on the
ribosomes. The impressive confirmation of this hypothetical model by biochemical
experimental evidence (see Rheinberger [1997]), greatly bolstered the genocentric
reductionist notion of the Central Dogma.
An early indication of the exhaustion of the notion that DNA sequences qualify
as genes only if they can produce a protein was Jacob and Monod’s [1961] model
of genetic regulation. At the face of it, the model of the genetic regulation of
the synthesis of lactose inEscherichia coli only bolstered the Central Dogma,
upholding the role of RNA as the messenger that conveys information from the
DNA sequence to the sequence of amino-acid in protein construction.
Jacob and Monod opened their paper stating: