Related Experiment Videos
Sequence specificity of the human mRNA N6-adenosine methylase in vitro
J E Harper1, S M Miceli, R J Roberts
1Department of Biological Sciences, Columbia University, New York, NY 10027.
Abstract:
N6-adenosine methylation is a frequent modification of mRNAs and their precursors, but little is known about the mechanism of the reaction or the function of the modification. To explore these questions, we developed conditions to examine N6-adenosine methylase activity in HeLa cell nuclear extracts. Transfer of the methyl group from S-[3H methyl]-adenosylmethionine to unlabeled random copolymer RNA substrates of varying ribonucleotide composition revealed a substrate specificity consistent with a previously deduced consensus sequence, Pu[G greater than A]AC[A/C/U]. 32-P labeled RNA substrates of defined sequence were used to examine the minimum sequence requirements for methylation. Each RNA was 20 nucleotides long, and contained either the core consensus sequence GGACU, or some variation of this sequence. RNAs containing GGACU, either in single or multiple copies, were good substrates for methylation, whereas RNAs containing single base substitutions within the GGACU sequence gave dramatically reduced methylation. These results demonstrate that the N6-adenosine methylase has a strict sequence specificity, and that there is no requirement for extended sequences or secondary structures for methylation. Recognition of this sequence does not require an RNA component, as micrococcal nuclease pretreatment of nuclear extracts actually increased methylation efficiency.
Insights
N6-adenosine methylation, a key RNA modification, is catalyzed by a specific enzyme. Researchers identified the precise sequence (GGACU) required for this methylation, revealing strict sequence specificity.
Area of Science:
- Molecular Biology
- Biochemistry
- Epigenetics
Background:
- N6-adenosine methylation is a prevalent mRNA modification with unknown functions and mechanisms.
- Understanding this modification is crucial for deciphering gene regulation and cellular processes.
Purpose of the Study:
- To investigate the mechanism and substrate specificity of N6-adenosine methylase activity.
- To determine the minimal sequence requirements for RNA methylation.
Main Methods:
- Utilized HeLa cell nuclear extracts to assay N6-adenosine methylase activity.
- Employed S-[3H methyl]-adenosylmethionine and various RNA substrates (random copolymers and defined sequences) to study methylation.
- Investigated the role of RNA secondary structure and protein components using micrococcal nuclease pretreatment.
Main Results:
- Identified a substrate specificity consistent with the consensus sequence Pu[G>A]AC[A/C/U].
- Demonstrated that the core GGACU sequence is essential for efficient methylation.
- Showed that single base substitutions within the GGACU sequence significantly reduce methylation efficiency.
- Found no requirement for extended sequences or secondary structures for methylation.
- Revealed that RNA component is not required for sequence recognition.
Conclusions:
- N6-adenosine methylase exhibits strict sequence specificity, recognizing the GGACU motif.
- Methylation efficiency is dependent on the presence and integrity of this specific sequence.
- The enzyme's recognition mechanism does not rely on RNA secondary structures or additional RNA components.