10.
D N A A N D R N A S Y N T H E S I S
341
from root meristem. From the similarity of the bimodal distributions
obtained for Feulgen stain (DNA) and Sakaguchi stain (arginine),
McLeish concluded that the D N A and bound arginine contained in
the nucleus increased closely together in his material. O n the other
hand, successive Feulgen stain and interferometric measurements on
ascites-tumour-cell nuclei (Richards and Davies, 1958) had previously
shown a bimodal distribution for the D N A values but a continuous
distribution for dry mass. From this the authors derived dissimilar
synthesis curves for D N A and nuclear protein which are equivalent to
those I have reported for tumour strain cells in culture (Seed, 1961,
1962, 1963a). Both the experiments quoted represent growth in vivo,
and both lend supporting evidence to the results shown in Figs. 6 and 7.
Considering these results on the relations between the synthetic
cycles of DNA, R N A and protein in rapidly dividing cells, it is perhaps
not surprising that Fautrez, Pisi and Cavalli (1955), Fautrez (1956) and
Frazer and Davidson (1953) found a correlation between D N A content
and nuclear volume within the same tissue for a variety of non-dividing
tissues. Again, the variability in cell size within the one tumour is well
known and is consistent with a dissociation of much of the nuclear
protein synthesis for a new cell from the synthesis of its D N A ; Moule
(1959) studied the ratio between nuclear protein and D N A content in
normal and cancerous liver, and found in the latter a wider dispersion
of values than in the normal tissue.
C . T H E C O N T R O L O F C E L L
M E T A B O L I S M
It is reasonable to suppose that at some time in the life of a normal
mammalian cell a "decision is made" either to differentiate or to
engage in a cycle of synthesis leading to a further division. It has been
known for some time (e.g. Howard and Pelc, 1953) that the result of
a decision in favour of division is manifested, as far as the genetic
material (DNA) is concerned, in the onset of D N A synthesis several
hours after telophase. As a result of the systematic quantitative investigations of the synthetic cycle described above, it now appears that the
same event also initiates simultaneously the bulk of the chromatin
R N A and protein syntheses for a new cell nucleus.
In the light of these results it is useful to recall recent studies on the
synthesis of D N A and R N A in vitro, already referred to on p . 320.
The work of Kornberg and his collaborators (1956; Lehman et al.,
1958; Bessman et al., 1958) has shown that the synthesis of D N A from
the four triphosphates requires the presence of a "primer" D N A and
that the base composition of the new D N A is similar to that of the old
(see p. 320). However, it appears that D N A extracted in the native,
D N A A N D R N A S Y N T H E S I S
341
from root meristem. From the similarity of the bimodal distributions
obtained for Feulgen stain (DNA) and Sakaguchi stain (arginine),
McLeish concluded that the D N A and bound arginine contained in
the nucleus increased closely together in his material. O n the other
hand, successive Feulgen stain and interferometric measurements on
ascites-tumour-cell nuclei (Richards and Davies, 1958) had previously
shown a bimodal distribution for the D N A values but a continuous
distribution for dry mass. From this the authors derived dissimilar
synthesis curves for D N A and nuclear protein which are equivalent to
those I have reported for tumour strain cells in culture (Seed, 1961,
1962, 1963a). Both the experiments quoted represent growth in vivo,
and both lend supporting evidence to the results shown in Figs. 6 and 7.
Considering these results on the relations between the synthetic
cycles of DNA, R N A and protein in rapidly dividing cells, it is perhaps
not surprising that Fautrez, Pisi and Cavalli (1955), Fautrez (1956) and
Frazer and Davidson (1953) found a correlation between D N A content
and nuclear volume within the same tissue for a variety of non-dividing
tissues. Again, the variability in cell size within the one tumour is well
known and is consistent with a dissociation of much of the nuclear
protein synthesis for a new cell from the synthesis of its D N A ; Moule
(1959) studied the ratio between nuclear protein and D N A content in
normal and cancerous liver, and found in the latter a wider dispersion
of values than in the normal tissue.
C . T H E C O N T R O L O F C E L L
M E T A B O L I S M
It is reasonable to suppose that at some time in the life of a normal
mammalian cell a "decision is made" either to differentiate or to
engage in a cycle of synthesis leading to a further division. It has been
known for some time (e.g. Howard and Pelc, 1953) that the result of
a decision in favour of division is manifested, as far as the genetic
material (DNA) is concerned, in the onset of D N A synthesis several
hours after telophase. As a result of the systematic quantitative investigations of the synthetic cycle described above, it now appears that the
same event also initiates simultaneously the bulk of the chromatin
R N A and protein syntheses for a new cell nucleus.
In the light of these results it is useful to recall recent studies on the
synthesis of D N A and R N A in vitro, already referred to on p . 320.
The work of Kornberg and his collaborators (1956; Lehman et al.,
1958; Bessman et al., 1958) has shown that the synthesis of D N A from
the four triphosphates requires the presence of a "primer" D N A and
that the base composition of the new D N A is similar to that of the old
(see p. 320). However, it appears that D N A extracted in the native,