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Geneticists and molecular biologists have been interested in
quantifying genes and their products for many years and for various
reasons (Bishop, 1974). Early molecular methods were based on
molecular hybridization, and were devised shortly after Marmur and
Doty (1961) first showed that denaturation of the double helix
could be reversed - that the process of molecular reassociation was
exquisitely sequence dependent. Gillespie and Spiegelman (1965)
developed a way of using the method to titrate the number of copies
of a probe within a target sequence in which the target sequence
was fixed to a membrane support prior to hybridization with the
probe - typically a RNA. Thus, this was a precursor to many of the
methods still in use, and indeed under development, today. Early
examples of the application of these methods included the
measurement of the copy numbers in gene families such as the
ribosomal genes and the immunoglo bulin family. Amplification of
genes in tumors and in response to drug treatment was discovered by
this method. In the same period, methods were invented for
estimating gene num bers based on the kinetics of the reassociation
process - the so-called Cot analysis. This method, which exploits
the dependence of the rate of reassociation on the concentration of
the two strands, revealed the presence of repeated sequences in the
DNA of higher eukaryotes (Britten and Kohne, 1968). An adaptation
to RNA, Rot analysis (Melli and Bishop, 1969), was used to measure
the abundance of RNAs in a mixed population."
Geneticists and molecular biologists have been interested in
quantifying genes and their products for many years and for various
reasons (Bishop, 1974). Early molecular methods were based on
molecular hybridization, and were devised shortly after Marmur and
Doty (1961) first showed that denaturation of the double helix
could be reversed - that the process of molecular reassociation was
exquisitely sequence dependent. Gillespie and Spiegelman (1965)
developed a way of using the method to titrate the number of copies
of a probe within a target sequence in which the target sequence
was fixed to a membrane support prior to hybridization with the
probe - typically a RNA. Thus, this was a precursor to many of the
methods still in use, and indeed under development, today. Early
examples of the application of these methods included the
measurement of the copy numbers in gene families such as the
ribosomal genes and the immunoglo bulin family. Amplification of
genes in tumors and in response to drug treatment was discovered by
this method. In the same period, methods were invented for
estimating gene num bers based on the kinetics of the reassociation
process - the so-called Cot analysis. This method, which exploits
the dependence of the rate of reassociation on the concentration of
the two strands, revealed the presence of repeated sequences in the
DNA of higher eukaryotes (Britten and Kohne, 1968). An adaptation
to RNA, Rot analysis (Melli and Bishop, 1969), was used to measure
the abundance of RNAs in a mixed population."
James D. Watson When, in late March of 1953, Francis Crick and I
came to write the first Nature paper describing the double helical
structure of the DNA molecule, Francis had wanted to include a
lengthy discussion of the genetic implications of a molecule whose
struc ture we had divined from a minimum of experimental data and
on theoretical argu ments based on physical principles. But I felt
that this might be tempting fate, given that we had not yet seen
the detailed evidence from King's College. Nevertheless, we reached
a compromise and decided to include a sentence that pointed to the
biological significance of the molecule's key feature-the
complementary pairing of the bases. "It has not escaped our
notice," Francis wrote, "that the specific pairing that we have
postulated immediately suggests a possible copying mechanism for
the genetic material." By May, when we were writing the second
Nature paper, I was more confident that the proposed structure was
at the very least substantially correct, so that this second paper
contains a discussion of molecular self-duplication using templates
or molds. We pointed out that, as a consequence of base pairing, a
DNA molecule has two chains that are complementary to each other.
Each chain could then act ." . . as a template for the formation on
itself of a new companion chain, so that eventually we shall have
two pairs of chains, where we only had one before" and, moreover, "
..."
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