NUCLEIC ACIDS AND SULPHYDRYL GROUPS
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These experiments have been repeated by Puiseux-Dao (1958) and, in
our laboratory by de Vitry (1962), who confirmed these
findings,
de Vitry (1962) also found that the effects of ribonuclease can be
reproduced by treatment of nucleate and anucleate fragments with
5,6-dichloro-j8-D-ribofuranosyl benzimidazole (DRB), a substance which
is known to effectively inhibit RNA synthesis in many biological
systems. Inhibition of regeneration is irreversible in anucleate, but
reversible in nucleate fragments. It is an interesting fact that, according
to de Vitry (1961, 1962), fluorodeoxyuridine (FUDR) and
fluorouridine
have a very different effect : these two pyrimidine analogs inhibit cap
formation (but not growth) in nucleate halves, while they have little
effect on morphogenesis in anucleate halves. Further analysis has shown
that FUDR inhibits first RNA and, later, protein synthesis. It is likely
that the analog has no effect on pre-existing RNA. Such an interpretation would offer a satisfactory explanation of the biological and biochemical observations.
Another series of experiments was performed in our laboratory
(Olszewska et al., 1961) using the technique of ultraviolet irradiation.
It was found that, in normal algae, uridine, adenine (and, as we have
already seen, methionine) are first incorporated into nuclear RNA and
protein; they are then distributed in the cytoplasm according to a
decreasing apico-basal gradient. After u.v. irradiation of the tip, cap
production and incorporation of these precursors in the apical region are
markedly decreased. Irradiation of the rhizoid has less effect on cap
production; it markedly reduces the incorporation, but without
modifying the apico-basal gradient. These results indicate that the
nucleus controls the synthesis of RNA and of the methionine-containing
protein ; these accumulate in the apical part of the alga, where they play
an important role in morphogenesis. Since u.v. radiation, at the wavelength used (2,537 Â) is, as a rule, much more effective in destroying
nucleic acids than proteins, the experiment indicates that, as we
suggested in 1957, RNA of nuclear origin and morphogenetic substances
are probably identical.
The same viewpoint, now also held by Hämmerling and his school, is
the basis of their own experiments with u.v. irradiation. For instance,
Richter (1959a, b) demonstrated that, in Acetabularia as in many other
cells, u.v. irradiation affects more directly RNA than protein synthesis ;
he found that u.v. inhibits net synthesis of RNA in nucleate fragments
during 16 days, while protein synthesis continues, but at a greatly
reduced rate. In anucleate halves, u.v. irradiation produces a decrease in
the RNA content and inhibits protein synthesis. More recently, Werz
and Hämmerling (1961) performed interesting experiments with interspecies grafts, combining u.v. irradiated and non-irradiated, nucleate
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271
These experiments have been repeated by Puiseux-Dao (1958) and, in
our laboratory by de Vitry (1962), who confirmed these
findings,
de Vitry (1962) also found that the effects of ribonuclease can be
reproduced by treatment of nucleate and anucleate fragments with
5,6-dichloro-j8-D-ribofuranosyl benzimidazole (DRB), a substance which
is known to effectively inhibit RNA synthesis in many biological
systems. Inhibition of regeneration is irreversible in anucleate, but
reversible in nucleate fragments. It is an interesting fact that, according
to de Vitry (1961, 1962), fluorodeoxyuridine (FUDR) and
fluorouridine
have a very different effect : these two pyrimidine analogs inhibit cap
formation (but not growth) in nucleate halves, while they have little
effect on morphogenesis in anucleate halves. Further analysis has shown
that FUDR inhibits first RNA and, later, protein synthesis. It is likely
that the analog has no effect on pre-existing RNA. Such an interpretation would offer a satisfactory explanation of the biological and biochemical observations.
Another series of experiments was performed in our laboratory
(Olszewska et al., 1961) using the technique of ultraviolet irradiation.
It was found that, in normal algae, uridine, adenine (and, as we have
already seen, methionine) are first incorporated into nuclear RNA and
protein; they are then distributed in the cytoplasm according to a
decreasing apico-basal gradient. After u.v. irradiation of the tip, cap
production and incorporation of these precursors in the apical region are
markedly decreased. Irradiation of the rhizoid has less effect on cap
production; it markedly reduces the incorporation, but without
modifying the apico-basal gradient. These results indicate that the
nucleus controls the synthesis of RNA and of the methionine-containing
protein ; these accumulate in the apical part of the alga, where they play
an important role in morphogenesis. Since u.v. radiation, at the wavelength used (2,537 Â) is, as a rule, much more effective in destroying
nucleic acids than proteins, the experiment indicates that, as we
suggested in 1957, RNA of nuclear origin and morphogenetic substances
are probably identical.
The same viewpoint, now also held by Hämmerling and his school, is
the basis of their own experiments with u.v. irradiation. For instance,
Richter (1959a, b) demonstrated that, in Acetabularia as in many other
cells, u.v. irradiation affects more directly RNA than protein synthesis ;
he found that u.v. inhibits net synthesis of RNA in nucleate fragments
during 16 days, while protein synthesis continues, but at a greatly
reduced rate. In anucleate halves, u.v. irradiation produces a decrease in
the RNA content and inhibits protein synthesis. More recently, Werz
and Hämmerling (1961) performed interesting experiments with interspecies grafts, combining u.v. irradiated and non-irradiated, nucleate
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