344
J . S E E D
Lajtha, Oliver, Kumatori and Ellis, 1958; Painter and Robertson,
1959; Yamada and Puck, 1961; Dickson, Paul and Davidson, 1958;
Kelly, Hirsch, Beach and Petrakis, 1957). On the other hand, an inhibition ofthe onset of mitosis is observed in both classes of cells.
Some years ago, it was reported that an increase in the u.v. absorption by the cytoplasm occurs in irradiated cells (Mitchell, 1942). More
recently, it was reported that an accumulation of soluble deoxyderivatives occurred in irradiated thymus, indicating that inhibition
of D N A synthesis by radiation was not caused by lack of precursors
(Bishop and Davidson, 1957; Main, Cole and Ellis, 1957; Ord and
Stocken, 1958). In addition, with the types of dividing cell showing
a presence or absence of radiosensitivity in regard to the onset of D N A
synthesis, there would seem to be a corresponding presence (thymus,
regenerating liver: Creasey and Stocken, 1958; Bollum, Anderegg,
McElya and Potter, 1960) or absence (ascites tumour, L-strain,
lymphosarcoma-strain cells: Paul, Dickson, Davidson and Smellie, 1960;
Klein and Forssberg, 1954) of radiosensitivity in regard to nuclear
phosphorylation. In this connexion, it is of interest that McEwen,
Allfrey and Mirsky (1961) showed from experiments with isolated
nuclei of calf thymus that the addition of histones to the reaction
mixture strongly inhibited nuclear phosphorylation. Davison and
Butler (1956) and Vendrely, Knobloch-Mazen and Vendrely (1960)
have also reported that the total amount of all the basic groups in the
nucleohistone is approximately equal to the total amount of phosphate
in the D N A .
Taking into account all the results quoted, it would seem that in
normal dividing cells, the association ofthe two radiosensitive processes,
onset of D N A synthesis and nuclear phosphorylation, would be consistent with a radiosensitivity ofthe process initiating "unblocking" of
the D N A template and thus enabling the cell to prepare for a further
division. On the other hand, in the tumour-strain cells, the lack of radiosensitivity of these two processes would be consistent with some kind of
permanent unblocking, by-passing the radiosensitive step, and similar
to that suggested from the studies on the cycles of R N A and nuclear
protein synthesis (Seed, 1961, 1962, 1963a, c ) .
R E F E R E N C E S
Alfert, M . (1950). A cytochemical study o f oogenesis and cleavage in the mouse.
J. cell. comp. Physiol 36, 381.
Astbury, W . T . (1947). X - r a y studies on nucleic acids. Symp. Soc. exp. Biol. \ , 66.
Avery, O . T . , M c L e o d , C . M . and M c C a r t y , M . (1944). Studies o n the chemical
nature o f the substance inducing transformation o f pneumococcal types. J. exp.
Med. 79, 137.
J . S E E D
Lajtha, Oliver, Kumatori and Ellis, 1958; Painter and Robertson,
1959; Yamada and Puck, 1961; Dickson, Paul and Davidson, 1958;
Kelly, Hirsch, Beach and Petrakis, 1957). On the other hand, an inhibition ofthe onset of mitosis is observed in both classes of cells.
Some years ago, it was reported that an increase in the u.v. absorption by the cytoplasm occurs in irradiated cells (Mitchell, 1942). More
recently, it was reported that an accumulation of soluble deoxyderivatives occurred in irradiated thymus, indicating that inhibition
of D N A synthesis by radiation was not caused by lack of precursors
(Bishop and Davidson, 1957; Main, Cole and Ellis, 1957; Ord and
Stocken, 1958). In addition, with the types of dividing cell showing
a presence or absence of radiosensitivity in regard to the onset of D N A
synthesis, there would seem to be a corresponding presence (thymus,
regenerating liver: Creasey and Stocken, 1958; Bollum, Anderegg,
McElya and Potter, 1960) or absence (ascites tumour, L-strain,
lymphosarcoma-strain cells: Paul, Dickson, Davidson and Smellie, 1960;
Klein and Forssberg, 1954) of radiosensitivity in regard to nuclear
phosphorylation. In this connexion, it is of interest that McEwen,
Allfrey and Mirsky (1961) showed from experiments with isolated
nuclei of calf thymus that the addition of histones to the reaction
mixture strongly inhibited nuclear phosphorylation. Davison and
Butler (1956) and Vendrely, Knobloch-Mazen and Vendrely (1960)
have also reported that the total amount of all the basic groups in the
nucleohistone is approximately equal to the total amount of phosphate
in the D N A .
Taking into account all the results quoted, it would seem that in
normal dividing cells, the association ofthe two radiosensitive processes,
onset of D N A synthesis and nuclear phosphorylation, would be consistent with a radiosensitivity ofthe process initiating "unblocking" of
the D N A template and thus enabling the cell to prepare for a further
division. On the other hand, in the tumour-strain cells, the lack of radiosensitivity of these two processes would be consistent with some kind of
permanent unblocking, by-passing the radiosensitive step, and similar
to that suggested from the studies on the cycles of R N A and nuclear
protein synthesis (Seed, 1961, 1962, 1963a, c ) .
R E F E R E N C E S
Alfert, M . (1950). A cytochemical study o f oogenesis and cleavage in the mouse.
J. cell. comp. Physiol 36, 381.
Astbury, W . T . (1947). X - r a y studies on nucleic acids. Symp. Soc. exp. Biol. \ , 66.
Avery, O . T . , M c L e o d , C . M . and M c C a r t y , M . (1944). Studies o n the chemical
nature o f the substance inducing transformation o f pneumococcal types. J. exp.
Med. 79, 137.