124
ALBERTO MONROY AND RACHELE MAGGIO
and protein-amino-acids. It is important to note that the increase of
RNA-nucleotide metabolism coincides with the rapidly ascending part
of the exponential respiratory curve. A contribution to the respiratory
increase may be made by the oxidation of glucose-6-phosphate
(Lindberg, 1943). The importance of ribose-phosphates in purine
metabolism is well known (Greenberg, 1951) and, therefore, a connection
between the increased metabolic activity of purines and of ribosephosphate on the one hand and of respiration on the other, may be
deduced (see Hultin, 1953e).
In the course of the last few years our knowledge of the metabolic
role of RNA in protein synthesis has considerably increased and several
functionally different types of RNA have been recognized. However,
nothing is known with regard to this question in the sea urchin embryo
and there is no need to emphasize how important such a study would be.
As has been mentioned, from fertilization to the 32-cell stage, RNA
metabolism, as measured by the incorporation of radioactive precursors
in the total RNA, is much lower than that of DNA. However, this does
not necessarily mean that all RNA fractions have a low metabolism.
Indeed the possibility must be considered of an actively incorporating,
small RNA fraction whose activity becomes diluted in the bulk of
relatively inactive RNA. Recent histo-autoradiographic work by Ficq,
Aiello and Scarano (personal communication) does indeed indicate an
active synthesis of nuclear RNA during early cleavage stages which the
above workers suggest might be a messenger RNA. This fraction might
be the one involved in the protein synthesis that also begins at
fertilization and reaches a peak at the 32- to 64-cell stage.
It is also pertinent to mention that Tocco, Orengo and Scarano
(personal communication) have studied the metabolism of RNA in the
subcellular fractions of the developing sea urchin embryo. They have
found that whereas total RNA does not change, an increase of the
nuclear and an equivalent decrease of the cytoplasmic RNA occurs in
the course of development. Using
3 2
P they have also shown that the
highest metabolic activity is in the nuclear RNA.
V. Some Notes on the Subcellular Components
A. The Nucleus
Much attention has been paid in recent years to the problem of the
role of the nucleus in the life-cycle of the cell and a number of important
data have been obtained. The most relevant among these is the
elucidation of the process whereby the genetic information encoded in
DNA is transmitted through the messenger RNA to the site of protein
synthesis, i.e., the microsomes. In fact, this result touches the very core
ALBERTO MONROY AND RACHELE MAGGIO
and protein-amino-acids. It is important to note that the increase of
RNA-nucleotide metabolism coincides with the rapidly ascending part
of the exponential respiratory curve. A contribution to the respiratory
increase may be made by the oxidation of glucose-6-phosphate
(Lindberg, 1943). The importance of ribose-phosphates in purine
metabolism is well known (Greenberg, 1951) and, therefore, a connection
between the increased metabolic activity of purines and of ribosephosphate on the one hand and of respiration on the other, may be
deduced (see Hultin, 1953e).
In the course of the last few years our knowledge of the metabolic
role of RNA in protein synthesis has considerably increased and several
functionally different types of RNA have been recognized. However,
nothing is known with regard to this question in the sea urchin embryo
and there is no need to emphasize how important such a study would be.
As has been mentioned, from fertilization to the 32-cell stage, RNA
metabolism, as measured by the incorporation of radioactive precursors
in the total RNA, is much lower than that of DNA. However, this does
not necessarily mean that all RNA fractions have a low metabolism.
Indeed the possibility must be considered of an actively incorporating,
small RNA fraction whose activity becomes diluted in the bulk of
relatively inactive RNA. Recent histo-autoradiographic work by Ficq,
Aiello and Scarano (personal communication) does indeed indicate an
active synthesis of nuclear RNA during early cleavage stages which the
above workers suggest might be a messenger RNA. This fraction might
be the one involved in the protein synthesis that also begins at
fertilization and reaches a peak at the 32- to 64-cell stage.
It is also pertinent to mention that Tocco, Orengo and Scarano
(personal communication) have studied the metabolism of RNA in the
subcellular fractions of the developing sea urchin embryo. They have
found that whereas total RNA does not change, an increase of the
nuclear and an equivalent decrease of the cytoplasmic RNA occurs in
the course of development. Using
3 2
P they have also shown that the
highest metabolic activity is in the nuclear RNA.
V. Some Notes on the Subcellular Components
A. The Nucleus
Much attention has been paid in recent years to the problem of the
role of the nucleus in the life-cycle of the cell and a number of important
data have been obtained. The most relevant among these is the
elucidation of the process whereby the genetic information encoded in
DNA is transmitted through the messenger RNA to the site of protein
synthesis, i.e., the microsomes. In fact, this result touches the very core