140
HERMAN
DENIS
B. Amount of Messenger RNA Synthesized
during Embryonic Development
The amount of mRNA synthesized by developing Xenopus embryos
was determined independently by Brown and Littna (1966a) and Denis
(1966b). In both determinations, the embryos were labeled by
3 2
P and
the specific activity of mRNA was estimated from that of the nucleoside monophosphates isolated from the acid-soluble pool of the embryos
(see Section IV).
Brown and Littna extracted the RNA from the embryos and eliminated
the low-molecular weight RNA (4 S and 5 S RNA) by passage on a
column of Sephadex G 100 (Fig. 17). The unretarded peak obtained
Tube no.
FIG. 17. Fractionation on Sephadex G 100 of the bulk RNA extracted from
embryos of various stages, which were exposed to
3 2
P from the beginning of development. The RNA used for each fractionation was extracted from 300 embryos. The
front peak, which contains most of the ultraviolet-absorbing material, is highmolecular-weight RNA. The second peak is low-molecular-weight RNA that was
retarded by the Sephadex. The numbers placed on top of each peak represent the
percentage of 2',3'-guanosine monophosphate + 2',3'-cytosine monophosphate contained in the RNA pooled from the fractions indicated by brackets.
0
-D.260 rryx
Radioactivity (cts/min)
2.0Late cleavage
Dorsal lip
Gastrula II hr
7 hr
9 hr
4
7
An
^
T
1
HERMAN
DENIS
B. Amount of Messenger RNA Synthesized
during Embryonic Development
The amount of mRNA synthesized by developing Xenopus embryos
was determined independently by Brown and Littna (1966a) and Denis
(1966b). In both determinations, the embryos were labeled by
3 2
P and
the specific activity of mRNA was estimated from that of the nucleoside monophosphates isolated from the acid-soluble pool of the embryos
(see Section IV).
Brown and Littna extracted the RNA from the embryos and eliminated
the low-molecular weight RNA (4 S and 5 S RNA) by passage on a
column of Sephadex G 100 (Fig. 17). The unretarded peak obtained
Tube no.
FIG. 17. Fractionation on Sephadex G 100 of the bulk RNA extracted from
embryos of various stages, which were exposed to
3 2
P from the beginning of development. The RNA used for each fractionation was extracted from 300 embryos. The
front peak, which contains most of the ultraviolet-absorbing material, is highmolecular-weight RNA. The second peak is low-molecular-weight RNA that was
retarded by the Sephadex. The numbers placed on top of each peak represent the
percentage of 2',3'-guanosine monophosphate + 2',3'-cytosine monophosphate contained in the RNA pooled from the fractions indicated by brackets.
0
-D.260 rryx
Radioactivity (cts/min)
2.0Late cleavage
Dorsal lip
Gastrula II hr
7 hr
9 hr
4
7
An
^
T
1