The Bin3 RNA methyltransferase targets 7SK RNA to control transcription and translation

Bicoid‐interacting protein 3 (Bin3) is a conserved RNA methyltransferase found in eukaryotes ranging from fission yeast to humans. It was originally discovered as a Bicoid (Bcd)‐interacting protein in Drosophila, where it is required for anterior–posterior and dorso‐ventral axis determination in the early embryo. The mammalian ortholog of Bin3 (BCDIN3), also known as methyl phosphate capping enzyme (MePCE), plays a key role in repressing transcription. In transcription, MePCE binds the non‐coding 7SK RNA, which forms a scaffold for an RNA–protein complex that inhibits positive‐acting transcription elongation factor b, an RNA polymerase II elongation factor. MePCE uses S ‐adenosyl methionine to transfer a methyl group onto the γ ‐phosphate of the 5′ guanosine of 7SK RNA generating an unusual cap structure that protects 7SK RNA from degradation. Bin3/MePCE also has a role in translation regulation. Initial studies in Drosophila indicate that Bin3 targets 7SK RNA and stabilizes a distinct RNA–protein complex that assembles on the 3′‐untranslated region of caudal mRNAs to prevent translation initiation. Much remains to be learned about Bin3/MeCPE function, including how it recognizes 7SK RNA, what other RNA substrates it might target, and how widespread a role it plays in gene regulation and embryonic development. WIREs RNA 2012 doi: 10.1002/wrna.1123 This article is categorized under: RNA Interactions with Proteins and Other Molecules > Protein–RNA Interactions: Functional Implications Translation > Translation Regulation RNA Processing > Capping and 5' End Modifications RNA in Disease and Development > RNA in Development