1 0 . D N A A N D R N A S Y N T H E S I S
333
these quantities continued to increase approximately together. However, in the cell types derived from or capable of producing tumours
(HeLa and L-strain) the increase in nuclear protein began before the
onset of D N A synthesis, and then appeared to proceed continuously.
Because of the genetic importance of DNA, it was suggested that the
difference in timing of nuclear protein synthesis between the normal
and tumour-strain cells reflected a fundamental difference in their
metabolisms (Seed, 1961, 1962).
In later work the measurements were extended to include the timing
of R N A synthesis in normal monkey kidney and HeLa cells (Seed,
1963a). This timing was ascertained by comparison of the curves for
the accumulation of total nuclear nucleic acid ( R N A + D N A from
u.v. absorption measurements) and for D N A (Feulgen stain). From
parallel RNAase and acid extractions, the R N A / D N A ratio appeared
to be in the region of 2:3 in the nuclei of both types of cells (ignoring
the nucleoli). For the nuclei of the monkey kidney cells (Fig. 2) the
averaged measurements showed that the dry mass, Feulgen (DNA) and
u.v. absorption ( R N A -f- DNA) values did not increase appreciably
until a delay of some 6 h had elapsed after telophase, and thereafter
these quantities increased approximately together. However, in the
HeLa cell nuclei (Fig. 3) the dry mass and u.v. absorption ( R N A -fDNA) increased approximately together in a continuous fashion during
interphase, in contrast with D N A synthesis which was discontinuous
in pattern.
From the results, it was concluded therefore that in the nuclei of
rapidly dividing monkey kidney cells the bulk of the R N A and nuclear
protein synthesis in the chromatin was associated with D N A synthesis,
whereas in the HeLa cells a large part of the chromatin R N A synthesis
(along with nuclear protein synthesis) was continuous throughout
interphase and was therefore not associated with D N A synthesis.
Separate plots of the Feulgen-stain measurements (DNA) and u.v.
absorption measurements ( R N A - f D N A ) for individual cell nuclei,
against the corresponding dry-mass values, confirmed the picture
shown by the timing data. For the monkey kidney cells, the dry mass,
D N A and total nucleic acid all increased approximately together
(Fig. 4). O n the other hand in the HeLa cells (Fig. 5) the total nucleic
acid and dry-mass values increased approximately together, but the
correlation between D N A and dry mass was appreciably worse: the
difference between the two correlations here is presumably due to the
continuous synthesis of R N A associated with the synthesis of protein,
as in Fig. 3.
Autoradiographic grain counts of the uptake of tritiated cytidine into
R N A and D N A of monkey kidney and HeLa cell nuclei were generally
333
these quantities continued to increase approximately together. However, in the cell types derived from or capable of producing tumours
(HeLa and L-strain) the increase in nuclear protein began before the
onset of D N A synthesis, and then appeared to proceed continuously.
Because of the genetic importance of DNA, it was suggested that the
difference in timing of nuclear protein synthesis between the normal
and tumour-strain cells reflected a fundamental difference in their
metabolisms (Seed, 1961, 1962).
In later work the measurements were extended to include the timing
of R N A synthesis in normal monkey kidney and HeLa cells (Seed,
1963a). This timing was ascertained by comparison of the curves for
the accumulation of total nuclear nucleic acid ( R N A + D N A from
u.v. absorption measurements) and for D N A (Feulgen stain). From
parallel RNAase and acid extractions, the R N A / D N A ratio appeared
to be in the region of 2:3 in the nuclei of both types of cells (ignoring
the nucleoli). For the nuclei of the monkey kidney cells (Fig. 2) the
averaged measurements showed that the dry mass, Feulgen (DNA) and
u.v. absorption ( R N A -f- DNA) values did not increase appreciably
until a delay of some 6 h had elapsed after telophase, and thereafter
these quantities increased approximately together. However, in the
HeLa cell nuclei (Fig. 3) the dry mass and u.v. absorption ( R N A -fDNA) increased approximately together in a continuous fashion during
interphase, in contrast with D N A synthesis which was discontinuous
in pattern.
From the results, it was concluded therefore that in the nuclei of
rapidly dividing monkey kidney cells the bulk of the R N A and nuclear
protein synthesis in the chromatin was associated with D N A synthesis,
whereas in the HeLa cells a large part of the chromatin R N A synthesis
(along with nuclear protein synthesis) was continuous throughout
interphase and was therefore not associated with D N A synthesis.
Separate plots of the Feulgen-stain measurements (DNA) and u.v.
absorption measurements ( R N A - f D N A ) for individual cell nuclei,
against the corresponding dry-mass values, confirmed the picture
shown by the timing data. For the monkey kidney cells, the dry mass,
D N A and total nucleic acid all increased approximately together
(Fig. 4). O n the other hand in the HeLa cells (Fig. 5) the total nucleic
acid and dry-mass values increased approximately together, but the
correlation between D N A and dry mass was appreciably worse: the
difference between the two correlations here is presumably due to the
continuous synthesis of R N A associated with the synthesis of protein,
as in Fig. 3.
Autoradiographic grain counts of the uptake of tritiated cytidine into
R N A and D N A of monkey kidney and HeLa cell nuclei were generally