This study investigates the methylation of mRNA in Novikoff hepatoma cells using poly(A) tract analysis. The authors labeled RNA with [1-3H]methionine and separated it using sucrose density gradient centrifugation to obtain mRNA. They then analyzed the composition of methylated nucleosides in the RNA using anion exchange chromatography and DEAE-cellulose (borate) chromatography. The results showed that about 50% of the radioactivity was recovered in the 2'-O-methyl nucleoside fraction, and the remaining 50% in the base-methyl nucleoside fraction. High-speed liquid chromatography of the 2'-O-methyl nucleoside fraction revealed four peaks corresponding to the four 2'-O-methyl nucleoside standards. The distribution of methylated nucleosides in mRNA was found to be predominantly N6-methyladenosine, which is simpler compared to the complex patterns observed in ribosomal RNA and tRNA. The study suggests that the presence of methylated nucleosides in mRNA may reflect a cellular mechanism for the selective processing of certain mRNA sequences, potentially playing a role in gene expression regulation.This study investigates the methylation of mRNA in Novikoff hepatoma cells using poly(A) tract analysis. The authors labeled RNA with [1-3H]methionine and separated it using sucrose density gradient centrifugation to obtain mRNA. They then analyzed the composition of methylated nucleosides in the RNA using anion exchange chromatography and DEAE-cellulose (borate) chromatography. The results showed that about 50% of the radioactivity was recovered in the 2'-O-methyl nucleoside fraction, and the remaining 50% in the base-methyl nucleoside fraction. High-speed liquid chromatography of the 2'-O-methyl nucleoside fraction revealed four peaks corresponding to the four 2'-O-methyl nucleoside standards. The distribution of methylated nucleosides in mRNA was found to be predominantly N6-methyladenosine, which is simpler compared to the complex patterns observed in ribosomal RNA and tRNA. The study suggests that the presence of methylated nucleosides in mRNA may reflect a cellular mechanism for the selective processing of certain mRNA sequences, potentially playing a role in gene expression regulation.