[Paper Review] A mutate-and-map protocol for inferring base pairs in structured RNA

Pablo Cordero, Wipapat Kladwang+2 more|arXiv (Cornell University)|Jan 31, 2013

RNA and protein synthesis mechanisms32 references4 citations

TL;DR

This paper introduces a mutate-and-map protocol that combines high-throughput mutagenesis with chemical mapping to infer base pairs in structured RNA. By systematically mutating nucleotides and measuring reactivity changes via capillary electrophoresis, the method reveals structural contacts, enabling accurate reconstruction of RNA secondary structure with single-nucleotide resolution and improved detection of non-canonical pairs.

ABSTRACT

Chemical mapping is a widespread technique for structural analysis of nucleic acids in which a molecule's reactivity to different probes is quantified at single-nucleotide resolution and used to constrain structural modeling. This experimental framework has been extensively revisited in the past decade with new strategies for high-throughput read-outs, chemical modification, and rapid data analysis. Recently, we have coupled the technique to high-throughput mutagenesis. Point mutations of a base-paired nucleotide can lead to exposure of not only that nucleotide but also its interaction partner. Carrying out the mutation and mapping for the entire system gives an experimental approximation of the molecules contact map. Here, we give our in-house protocol for this mutate-and-map strategy, based on 96-well capillary electrophoresis, and we provide practical tips on interpreting the data to infer nucleic acid structure.

Motivation & Objective

• To develop a scalable experimental method for determining RNA secondary structure by combining mutagenesis with chemical mapping.
• To improve the accuracy of base pair inference in structured RNAs, especially for non-canonical pairs.
• To provide a practical, reproducible workflow using 96-well capillary electrophoresis for high-throughput data collection.
• To enable systematic probing of structural perturbations caused by point mutations in base-paired regions.
• To offer interpretative guidelines for mapping data to deduce RNA contact maps and structural constraints.

Proposed method

• The protocol uses site-directed mutagenesis to individually mutate each nucleotide in a structured RNA.
• Each mutant is subjected to chemical probing with reagents like DMS or CMCT to assess reactivity at single-nucleotide resolution.
• Reactivity data from mutants are collected using 96-well capillary electrophoresis for high-throughput quantification.
• Changes in reactivity upon mutation are interpreted as indicators of structural context, particularly loss of protection in base-paired regions.
• Mutant reactivity profiles are used to infer base pairing by identifying compensatory changes in reactivity between putative partners.
• The method leverages the principle that mutation of a base-paired nucleotide can expose both the mutated base and its partner, altering their reactivity.

Experimental results

Research questions

• RQ1 How can high-throughput mutagenesis be integrated with chemical mapping to infer RNA secondary structure?
• RQ2 What reactivity changes occur in base-paired nucleotides upon point mutation, and how do they reveal structural context?
• RQ3 Can this approach reliably detect non-canonical base pairs and structural rearrangements?
• RQ4 How can reactivity data from multiple mutants be systematically interpreted to reconstruct a contact map?
• RQ5 What experimental and analytical parameters are critical for accurate base pair inference using this method?

Key findings

• The mutate-and-map approach successfully identifies base pairs in structured RNAs by detecting reactivity changes upon mutation, with increased reactivity observed in both the mutated nucleotide and its pairing partner.
• The method enables detection of non-canonical base pairs that may be missed by traditional chemical probing alone.
• Capillary electrophoresis in a 96-well format allows robust, high-throughput data collection with reproducible reactivity measurements.
• Mutant reactivity profiles reveal structural perturbations consistent with known RNA structures, validating the approach.
• The protocol provides a systematic framework for interpreting chemical mapping data in the context of mutational effects on base pairing.
• The approach improves the resolution and accuracy of RNA structure modeling by integrating mutational and probing data.