The uncapped and capped RNA samples were desalted with ammonium acetate precipitation to replace the Na+ on the RNA backbone56 (link). The desalted RNA samples were dissolved in ultrapure water to 20 μM and analyzed with direct infusion method on a Q exactive plus orbitrap mass spectrometer (ThermoFisher Scientific) on negative mode with 70,000 resolving power at 200 m/z. 100 scans were acquired to improve the S/N.
SAM/SAH standard mixture and freshly purified MePCEMT protein were analyzed on ZORBAX C3 column 3.0×150 mm with bead size 3.5 μm (Agilent Technologies) using Agilent 6530 Q-TOF ESI with a 1260 Infinity LC. Buffer A and B were 0.1% formic acid in water and 0.1% formic acid in acetonitrile, respectively. A linear gradient from 1–99% B was applied for a duration of 8 min and elutions were analyzed on positive mode of ESI-TOF mass spectrometer.
SAM/SAH standard mixture and freshly purified MePCEMT protein were analyzed on ZORBAX C3 column 3.0×150 mm with bead size 3.5 μm (Agilent Technologies) using Agilent 6530 Q-TOF ESI with a 1260 Infinity LC. Buffer A and B were 0.1% formic acid in water and 0.1% formic acid in acetonitrile, respectively. A linear gradient from 1–99% B was applied for a duration of 8 min and elutions were analyzed on positive mode of ESI-TOF mass spectrometer.