Inhibitory effect of ammonium chloride and chloroquine on the entry of the toxic lectin modeccin into HeLa cells

Ammonium chloride and chloroquine protected a variety of cell lines against diphtheria toxin and the toxic lectin modeccin. Experiments where the ability of antibody to neutralize the toxin was measured indicate that in the presence of ammonium chloride and chloroquine, modeccin remains at the cell surface and that the two compounds inhibit the uptake of modeccin into the cytoplasm. A cell line tolerating increased concentrations of modeccin was not protected against modeccin by ammonium chloride or chloroquine, whereas the compounds did protect these cells against diphtheria toxin.     

Translation of enzymically decapped messenger RNA.

An enzymic procedure was used to remove the 7-methylguanosine diphosphate moiety at the 5' ends of rabbit hemoglobin mRNA and mouse immunoglobulin light-chain mRNA. Evidence was obtained that the procedure, which involves the use of polynucleotide kinase, does not result in any further degradation of the mRNA. The enzymically decapped mRNA was as effective as untreated mRNA in supporting protein synthesis in a wheat germ system. This was the case over a wide range of mRNA concentrations and over a considerable period of time. The presence in the incubation mixture of S-adenosylhomocysteine, an inhibitor of methylation, did not affect the results. The data indicate that the presence of a 7-methylguanosine diphosphate residue at the 5' end of mRNAs is not an obligatory requirement for translation in eucaryotic systems.