The basic properties of mRNA-injected Xenopus oocytes as a heterologous system for the production of biologically active proteins will be reviewed. The advantages and limitations involved in the use of this in ovo system will be discussed, as compared with in vitro cell-free translation systems and with in vivo microinjected mammalian cells in culture. The different assay systems that have been utilized for the identification of the biological properties of oocyte-produced proteins will be described. This section will review the determination of properties such as binding of natural ligands, like heme or alpha-bungarotoxin; immunological recognition by antibodies; subcellular compartmentalization and/or secretion; various enzymatic catalytic activities; and induction in ovo of biological activities that affect other living cells in culture, such as those of interferon and of the T-cell receptor. The limitations involved in interpretation of results obtained using mRNA-injected oocytes will be critically reviewed. Special attention will be given to the effect of oocyte proteases and of changes in the endogenous translation rate on quantitative measurements of oocyte-produced proteins. In addition, the validity of the various measurement techniques will be evaluated. The various uses of bioassays of proteins produced in mRNA-injected Xenopus oocytes throughout the last decade will be reviewed. Nuclear and cytoplasmic injections, mRNA and protein turnover measurements and abundance calculations, and the use of in ovo bioassays for molecular cloning experiments will be discussed in this section. Finally, potential future uses of the oocyte system in various fields of research, such as immunology, neurobiology, and cell biology will be suggested.

The biosynthesis of biologically active proteins in mRNA-microinjected Xenopus oocytes.

The polypeptide precursor pr76 to the internal viral group specific (gs) antigen proteins of Rous sarcoma virus, synthesized in a cell-free system of ascites cells, has been pro- cessed in vitro into the viral proteins by purified viral protein p15 as well as by disrupted Rous sarcoma virus. Disrupted Rauscher murine leukemia virus does not stimulate the cleavage process in vitro. Autocatalytic cleavage of the polypeptide precursor pr76 of Rous sarcoma virus, which contains the pep- tide sequence of p15, is not observed. Virus specific proteins of several RNA viruses (polio virus, en- domyocarditis virus, (1-4), Sindbis virus, Semliki Forest virus (5-8), and RNA tumor viruses (9-12)) are derived from larger polypeptide precursors by post-translational cleavage. Little is known about the agents involved in the cleavage process. Undefined proteolytic activity has been observed in several purified animal virions (vesicular stomatitis virus, influenza virus, and mengovirus) (13). For polio virus, precursors have - ~~~~~~~~ p19 a '~~~~~~-p12/1 ..Y.^,~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~.. .... .. .. ..

Cleavage of Rous sarcoma viral polypeptide precursor into internal structural proteins in vitro involves viral protein p15 Iviral precursor polypeptide/group-specific (gs) antigen/in vitro proteolytic cleavage process)

Thyroglobulin is a 19S protein of approxi- mately 660,000 daltons and unknown quaternary structure.We have previously shown that a 33S mRNA purified from mammalian thyroids promoted synthesis in the Xenopusoocyte of a peptide immunologically related to thyroglobu- lin. Chemical identity to the native protein is now presentedby means of a tryptic peptide analysis. Moreover, the 33SmRNAis shown to contain all the information required forthe synthesis of a complete 19S thyroglobulin molecule. Gelfiltration in Sepharose under denaturing conditions indicates that the reduced polypeptide encoded by the 33S mRNAis largerthan 210,000 aons. A modelof adimeric thyroglobu-lin withabout 300,000 daltonsubunits is presented.Thyroglobulinis ahugemultimericglycoprotein ofapproxi-mately 600,000 daltons and a sedimentation coefficient of19 S (1). It is the major product of protein synthesis by the thyroid gland (2), which after iodination and coupling of afraction of its tyrosyl residues, serves as storage for inactivethyroid hormones. Avery specific structure of the moleculeis required to allow efficient coupling of iodotyrosines intothe hormonal iodothyronine moieties. Indeed, when com-pared with other iodoproteins, iodinated thyroglobulin

Translation ofthyroglobulin 33Smessenger RNA asameansof determining thyroglobulin quaternary structure

Carp proinsulin and rabbit globin, synthesized in Xenopus oocytes in response to simultaneously injected mRNAs, are found in membrane vesicles and in the cytosol respectively. After 24 h of incubation labeled proinsulin, but not globin, is found also in the medium, indicating specific secretion from the oocytes. No insulin could be found either within or outside the oocytes. The results provide further evidence that the mRNA for a given protein contains the information for its intracellular destination and its eventual secretion.

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1432-1033.1981.tb06254.x

Intracellular compartmentation and secretion of carp proinsulin synthesized in Xenopus oocytes.

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1016/0014-5793%2881%2980104-4

Secreted proteins in the medium of microinjected Xenopus oocytes are degraded by oocyte proteases.

The genetic information carried by eukaryotic messenger RNAs can be translated to polypeptides either in cell-free protein synthesizing systems or after microinjection into living cells.

Expression of Messenger RNAs Injected into Xenopus Laevis Oocytes

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Expression of Messenger RNAs Injected into Xenopus Laevis Oocytes