270
JEAN BRÄCHET
They are absent from the middle part of the stalk, which is incapable of
producing a cap. Werz (1959) concludes that these proteins are probably
synthesized under the action of the 'morphogenetic substances' and that
they must play a role in the formation of the sterile whorls and caps.
We have recently made observations (Brächet, unpublished) which are
strikingly similar to those of Werz (1959), by staining living algae with
dilute solutions of toluidine blue. A metachromatic staining occurs at the
apex of the stalk and its intensity is related to the growth-rate of the
whole algae or fragments.
Finally, good evidence has been found for the view that proteins
originating from the nucleus accumulate at the tip of the alga
(Olszewska and Brächet, 1961): using
35
£-methionine as a label and an
autoradiographic technique for detection, it was found that a methioninecontaining protein is first synthesized in the nucleus. It then migrates
into the cytoplasm and accumulates at the tip of the alga. Synthesis of a
methionine-containing protein in the nucleus and its subsequent passage
to the cytoplasm had already been found in amoebae by Goldstein
(1958), but, in this case, the protein is of course not fixed to a specific
receptor such as the apical extremity of Acetabularia,
and it migrates
back to the nucleus. Whether or not the methionine-containing protein
of nuclear origin of Olszewska and Brächet (1961) and the azocarminestaining proteins of Werz (1959) are identical remains unknown.
It is of course unlikely, on theoretical grounds, that the methioninecontaining proteins of Acetabularia carry genetic information from the
nucleus to the cytoplasm. It is a possibility that these proteins are
associated with nuclear RNA, which is a much more likely candidate for
the bearer of information between the genes and the genetically determined character, i.e., the cap. The role of the methionine-containing
protein might be to combine with nuclear (messenger) RNA and to
protect it from breakdown by catabolic enzymes present in the
cytoplasm.
2. RNA as an Intermediary Between the Nucleus
and the Genetically Determined Cap
The most impressive experiments, in this field, are those of Stich and
Plaut (1958), who treated in vivo nucleate and anucleate fragments with
ribonuclease. They found that the enzyme inhibits regeneration and
protein synthesis in both nucleate and anucleate halves. But, whereas
the inhibition is irreversible in the anucleate fragments, it is reversible
in the nucleate ones. These facts strongly suggest that the destruction of
pre-existing RNA by the ribonuclease treatment inhibits morphogenesis ;
only the nucleate fragments can replace the RNA, when they are placed
in normal sea-water.
JEAN BRÄCHET
They are absent from the middle part of the stalk, which is incapable of
producing a cap. Werz (1959) concludes that these proteins are probably
synthesized under the action of the 'morphogenetic substances' and that
they must play a role in the formation of the sterile whorls and caps.
We have recently made observations (Brächet, unpublished) which are
strikingly similar to those of Werz (1959), by staining living algae with
dilute solutions of toluidine blue. A metachromatic staining occurs at the
apex of the stalk and its intensity is related to the growth-rate of the
whole algae or fragments.
Finally, good evidence has been found for the view that proteins
originating from the nucleus accumulate at the tip of the alga
(Olszewska and Brächet, 1961): using
35
£-methionine as a label and an
autoradiographic technique for detection, it was found that a methioninecontaining protein is first synthesized in the nucleus. It then migrates
into the cytoplasm and accumulates at the tip of the alga. Synthesis of a
methionine-containing protein in the nucleus and its subsequent passage
to the cytoplasm had already been found in amoebae by Goldstein
(1958), but, in this case, the protein is of course not fixed to a specific
receptor such as the apical extremity of Acetabularia,
and it migrates
back to the nucleus. Whether or not the methionine-containing protein
of nuclear origin of Olszewska and Brächet (1961) and the azocarminestaining proteins of Werz (1959) are identical remains unknown.
It is of course unlikely, on theoretical grounds, that the methioninecontaining proteins of Acetabularia carry genetic information from the
nucleus to the cytoplasm. It is a possibility that these proteins are
associated with nuclear RNA, which is a much more likely candidate for
the bearer of information between the genes and the genetically determined character, i.e., the cap. The role of the methionine-containing
protein might be to combine with nuclear (messenger) RNA and to
protect it from breakdown by catabolic enzymes present in the
cytoplasm.
2. RNA as an Intermediary Between the Nucleus
and the Genetically Determined Cap
The most impressive experiments, in this field, are those of Stich and
Plaut (1958), who treated in vivo nucleate and anucleate fragments with
ribonuclease. They found that the enzyme inhibits regeneration and
protein synthesis in both nucleate and anucleate halves. But, whereas
the inhibition is irreversible in the anucleate fragments, it is reversible
in the nucleate ones. These facts strongly suggest that the destruction of
pre-existing RNA by the ribonuclease treatment inhibits morphogenesis ;
only the nucleate fragments can replace the RNA, when they are placed
in normal sea-water.