Abstract
CGG tandem repeat expansion in the 5′-untranslated region of the fragile X mental retardation-1 (FMR1) gene leads to unusual nucleic acid conformations, hence causing genetic instabilities. We show that the number of G…G (in CGG repeat) or C…C (in CCG repeat) mismatches (other than A…T, T…A, C…G and G…C canonical base pairs) dictates the secondary structural choice of the sense and antisense strands of the FMR1 gene and their corresponding transcripts in fragile X-associated tremor/ataxia syndrome (FXTAS). The circular dichroism (CD) spectra and electrophoretic mobility shift assay (EMSA) reveal that CGG DNA (sense strand of the FMR1 gene) and its transcript favor a quadruplex structure. CD, EMSA and molecular dynamics (MD) simulations also show that more than four C…C mismatches cannot be accommodated in the RNA duplex consisting of the CCG repeat (antisense transcript); instead, it favors an i-motif conformational intermediate. Such a preference for unusual secondary structures provides a convincing justification for the RNA foci formation due to the sequestration of RNA-binding proteins to the bidirectional transcripts and the repeat-associated non-AUG translation that are observed in FXTAS. The results presented here also suggest that small molecule modulators that can destabilize FMR1 CGG DNA and RNA quadruplex structures could be promising candidates for treating FXTAS.
Highlights
The eukaryotic genome comprises ubiquitous repetitive sequences, namely microsatellites
We investigate the secondary structural choice of CCG and CGG repeats from the perspective of addressing the molecular basis of fragile X-associated tremor/ataxia syndrome (FXTAS) by employing molecular dynamics (MD) simulations, circular dichroism (CD), and electrophoretic mobility shift assay (EMSA)
MD, EMSA, and CD investigations have been carried out to explore the association between the repeat number and secondary structural preference for the DNA and RNA sequences consisting of the CGG and CCG repeats (Table 1)
Summary
The eukaryotic genome comprises ubiquitous repetitive sequences, namely microsatellites. When the number of trinucleotide repeats exceeds the threshold, it forms an unusual nucleic acid conformations[4] One such example is CGG trinucleotide repeat expansion in the fragile X mental retardation-1 (FMR1) gene. The antisense CCG strand favors the hairpin structure, the antisense transcript prefers the i-motif/i-motif conformational intermediate structure Such a noncanonical secondary structural choice may be the underlying molecular cause for the RNA misprocessing in FXTAS. The mechanism proposed here, which is based on the secondary structural choice of CGG (quadruplex) and CCG (i-motif/i-motif conformational intermediate) repeats, explains the neurotoxicity observed in FXTAS
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
