Injected amphibian oocytes: a living test tube for the study of eukaryotic gene transcription?

Somatic-cell nuclei injected in Xenopus laevis oocytes remain transcriptionally active for up to 4 weeks. The rate of RNA synthesis increases as the somatic-cell nuclei enlarge. The message activity of the RNA synthesized by the injected nuclei can be demonstrated, as new proteins are made a few days after injection of HeLa-cell nuclei.

Injected nuclei in frog oocytes:RNA synthesis and protein exchange.

Nuclei from HeLa and other mammalian cells have been injected into Xenopus oocytes. The synthesis, uptake, and release of RNA and proteins by injected nuclei have been investigated by autoradiography. Injected nuclei which undergo enlargement synthesize RNA continuously for up to 28 days.

High tyrosinase activity in albino Xenopus laevis oocytes.

Tyrosinase was measured in oocytes of the recently described albino mutant (apap) of Xenopus laevis. Although these oocytes show no pigmentation and the eggs are known to contain no melanosomes, tyrosinase - which is probably the only enzyme necessary for melanin synthesis from tyrosine - was increased more than twofold relative to the wild type. Tyrosinase recovered from albino and wild type oocytes showed the same Km with respect to tyrosine, and this was not altered by previous gonadotrophin stimulation in vivo.

Effect of adrenergic agonists on phosphatidylinositol labelling in heart and aorta.

(1) The metabolism of phosphatidylinositol has been investigated in heart fragments and aorta slices incubated with adrenergic agonists. (2) Noradrenaline and isoprenaline had no stimulatory effect on 32Pi incorporation into phosphatidylinositol in cat and guinea-pig hearts. (3) Incorporation of 32Pi into phosphatidylinositol was enhanced by noradrenaline and methoxamine in cat aorta.

Regulation of uracil uptake in Escherichia coli by adenosine 3',5'-monophosphate.

Culture of a wild-type strain of Escherichia coli in the presence of cyclic AMP leads to an impairment of uracil uptake. Half maximum inhibition of uracil uptake was observed at 1.5 mM cyclic AMP.

Injected nuclei in frog oocytes provide a living cell system for the study of transcriptional control.

Human HeLa nuclei injected into Xenopus oocytes synthesise RNA continuously for up to 1 month, and some of this RNA is translated into HeLa proteins. Nuclear proteins extracted from other cells enter the injected nuclei. This living cell system can be used for the study of transcriptional controls.

The incorporation of hydrophobic protein receptors and artificial lipid membranes.

The mechanism of chemical synaptic transmission implies: 1) the existence of a specific protein receptor at the postsynaptic membrane, and 2) the interaction between the transmitter released and the receptor, thus producing a change in ionic permeability. Previous studies from our laboratory have shown that special hydrophobic proteins extracted from postsynpatic membranes of different tissues showed a high affinity binding for the different pharmacological agents. The present paper describes experiments in which different hydrophobic protein binding acetylcholine, noradrenaline, gamma-aminobutyric acid, and glutamate were incorporated into artificial lipid membranes, similar to those first described by Mueller et al.

Subcellular distribution and possible role of gangliosides in the CNS.

From cell fractionation studies it is concluded that gangliosides have a wide distribution in neuronal plasma membranes, being concentrated in the microsomal and the nerve-ending membranes rich in acetylcholinesterase. When properly purified synaptic vesicles are devoid of gangliosides and acetylcholinesterase; thus the possible relationship between gangliosides and the cholinergic transmitter should be discarded. There are important evidences that specific gangliosides may play a role in the binding of certain toxins and viruses to the plasma membrane; however, their possible role as synaptic receptors is not supported by our experiments.