Über die Frage der Mehrdeutigkeit des genetischen Codes, untersucht am Hüllenprotein des Tabakmosaikvirus

Summary

An investigation has been made of whether ambiguity of the genetic code, i.e. variation in the translation of the genetic message produced by some external factors, occurs in tobacco plants infected with tobacco mosaic virus (TMV). This effect ist known to occur in bacterial systems.

The following experiments have been done: a) TMV-vulgare infected plants were kept at five different temperatures between the minimum (12°C) and maximum (37°C) of the virus multiplication. b) TMV-A14 was grown in leaves in the presence of high concentrations of each of the following three cations: streptomycin, spermine, Mg⁺⁺. c) Plants infected with the TMV mutant Ni 1927 were kept under the same conditions as in and b.

After isolation of the virus the following proteinchemical methods were applied to the virus preparations which were grown under the eight conditions mentioned above: a) Amino acid analyses of the whole coat protein of TMV vulgare, b) separation of the RNA from the coat protein of vulgare and A 14, digestion of the proteins with trypsin, isolation of all tryptic peptides by column and paper chromatography, hydrolysis and analysis of the amino acid composition of each peptide, c) quantitative determinations of the terminal amino acids split off by treatment of Ni 1927 with carboxypeptidase A.

The analyses of all virus preparations gave the same results: within the experimental errors (1–2% and 5% depending on the method) there is no variation in the amino acid compositions of the tryptic peptides as a consequence of the various polycations or temperatures. The same result has been found with X-protein isolated from leaves in which the virus was synthesized in the presence of streptomycin.

From the foregoing analyses it was concluded that translation of the genetic information into the amino acid sequence of TMV protein is influenced, if at all, to such a low extent that this effect cannot be found by the current methods of proteinchemistry.