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Existence of Internal N7‑Methylguanosine Modification in mRNA Determined by Differential Enzyme Treatment Coupled with Mass Spectrometry Analysis
journal contribution
posted on 2018-01-09, 00:00 authored by Jie-Mei Chu, Tian-Tian Ye, Cheng-Jie Ma, Meng-Dan Lan, Ting Liu, Bi-Feng Yuan, Yu-Qi FengThe
recent discovery of reversible chemical modifications on mRNA
has opened a new era of post-transcriptional gene regulation in eukaryotes.
Among the 15 types of modifications identified in mRNA of eukaryotes, N7-methylguanosine (m7G) is unique owing to its
presence in the 5′ cap structure. It remains unknown whether
m7G is also present internally in mRNA, and this is largely
attributed to the lack of an appropriate analytical method to differentiate
internal m7G in mRNA from that in the 5′ cap. To
address this analytical challenge, we developed a novel strategy of
combining differential enzymatic digestion with liquid chromatography–tandem
mass spectrometry analysis to quantify the levels of these two types
of m7G modifications in mRNA. In particular, we found that
S1 nuclease and phosphodiesterase I exhibit differential activities
toward internal and 5′-terminal m7G. By using this
method, we found that internal m7G was present in mRNA
of cultured human cells as well as plants and rat tissue. In addition,
our results showed that plants contain higher levels of internal m7G in mRNA than mammals. We also observed that exposure of
rice to cadmium (Cd) stimulated marked diminution in the levels of
m7G at both the 5′ cap and internal positions of
mRNA, which was correlated with the Cd-induced elevated expression
of m7G-decapping enzymes. Taken together, we reported here
a strategy to distinguish internal and 5′-terminal m7G in mRNA, and by using this method, we demonstrated the prevalence
of internal m7G modification in mRNA, which we believe
will stimulate future functional studies of m7G on post-transcriptional
gene regulation in eukaryotes.