Editing Messenger RNA (section)

=== mRNA circularization ===
[[File:Fgene-10-00006-g001.jpg|thumb|mRNA circularisation and regulation]]
In eukaryotes mRNA molecules form circular structures due to an interaction between the [[eIF4E]] and [[poly(A)-binding protein]], which both bind to [[eIF4G]], forming an mRNA-protein-mRNA bridge.<ref>{{cite journal | vauthors = Wells SE, Hillner PE, Vale RD, Sachs AB | title = Circularization of mRNA by eukaryotic translation initiation factors | journal = Molecular Cell | volume = 2 | issue = 1 | pages = 135–140 | date = July 1998 | pmid = 9702200 | doi = 10.1016/S1097-2765(00)80122-7 | citeseerx = 10.1.1.320.5704 }}</ref> Circularization is thought to promote cycling of ribosomes on the mRNA leading to time-efficient translation, and may also function to ensure only intact mRNA are translated (partially degraded mRNA characteristically have no m7G cap, or no poly-A tail).<ref>{{cite journal | vauthors = López-Lastra M, Rivas A, Barría MI | title = Protein synthesis in eukaryotes: the growing biological relevance of cap-independent translation initiation | journal = Biological Research | volume = 38 | issue = 2–3 | pages = 121–146 | year = 2005 | pmid = 16238092 | doi = 10.4067/S0716-97602005000200003 | doi-access = free }}</ref>

Other mechanisms for circularization exist, particularly in virus mRNA. [[Poliovirus]] mRNA uses a cloverleaf section towards its 5' end to bind PCBP2, which binds [[poly(A)-binding protein]], forming the familiar mRNA-protein-mRNA circle. [[Barley yellow dwarf virus]] has binding between mRNA segments on its 5' end and 3' end (called kissing stem loops), circularizing the mRNA without any proteins involved.

RNA virus genomes (the + strands of which are translated as mRNA) are also commonly circularized.<ref>{{cite journal | vauthors = Zhang X, Liang Z, Wang C, Shen Z, Sun S, Gong C, Hu X | title = Viral Circular RNAs and Their Possible Roles in Virus-Host Interaction | journal = Frontiers in Immunology | volume = 13 | pages = 939768 | date = 2022 | pmid = 35784275 | pmc = 9247149 | doi = 10.3389/fimmu.2022.939768 | doi-access = free }}</ref> During genome replication the circularization acts to enhance genome replication speeds, cycling viral RNA-dependent RNA polymerase much the same as the ribosome is hypothesized to cycle.