Effect of introduction of small alkyl groups on mRNA function.

Treatment of RNA with dimethyl sulfate methylates only nitrogens, preferentially the 7 position of guanosine, whereas treatment with ethylnitrosourea ethylates mainly oxygens, preferentially the phosphodiester groups. Two plant viral mRNAs were modified with these two reagents at levels of 4-28 alkylations per molecule. The ability of alkylated RNAs to stimulate amino acid incorporation in the wheat germ system was somewhat diminished by both types of modification, but the predominant protein made, as ascertained by polyacrylamide gel electrophoresis, was the typical gene product of the respective mRNA. These data suggest that random alkylations, mostly of either the guanosine N-7s or the phosphates, do not interfere with peptide chain elongation, but that the ability to initiate translation properly is affected by these substitutions, presumably through their effect on the conformation of the RNAs.