Table 2.

Mass transitions of 7‐methylguanosine isotopomers in pulse‐chase NAIL‐MS for RNA repair observation.

Nucleoside	Labeling[a]	Precursor[b]	Product[c]	t R [min]
guanosine	unlabeled[d]	284	152	3.7
	15N‐label[e]	289	157	3.7
	SIL‐IS[f]	299	162	3.7
7‐methylguanosine	unlabeled	298	166	2.0
	CD3‐label[g]	301	169	2.0
	15N/CD3‐label[e]	306	174	2.0
	SIL‐IS	314	177	2.0

[a] Used labeling technique. [b] Precursor ion m/z. [c] Product ion m/z. [d] No labeled metabolites, original nucleosides. [e] tRNA transcribed in the presence of ¹⁵N, de novo nucleosides. [f] SIL‐IS: stable isotope labeled internal standard prepared from a complete ¹³C/¹⁵N‐labeled E. coli culture. [g] Labeling with CD₃‐methionine to detect enzymatic methylation of original nucleoside, methylated after stress.