Dual modes of ZFC3H1 confer selectivity in nuclear RNA sorting

Area of Science:

• Molecular Biology
• RNA Biology
• Gene Regulation

Background:

• Nuclear RNA processing involves competing export and degradation pathways.
• The exosome cofactor poly(A) exosome targeting (PAXT) complex directs mature RNAs to degradation.
• Distinguishing RNAs destined for degradation from those for translation is a challenge.

Purpose of the Study:

• To elucidate the mechanism by which ZFC3H1 regulates RNA fate.
• To understand how RNA features influence the recruitment and activation of PAXT components.
• To clarify the interplay between RNA export and degradation pathways.

Main Methods:

• Co-transcriptional loading assays of ZFC3H1 onto pre-RNAs.
• Conformational analysis of ZFC3H1 in different RNA contexts.
• Investigating the role of transient PAXT components (ZC3H3, RBM26/27) in RNA processing.
• Assessing the impact of RNA length and exon number on ZFC3H1 activation and RNA fate.

Main Results:

• ZFC3H1 is co-transcriptionally loaded onto nascent RNA precursors in an inactive, "closed" conformation.
• This initial loading does not trigger degradation, as exosome recruitment is blocked.
• RNA length and exon number dictate subsequent ZFC3H1 activation and recruitment of other PAXT factors.
• Shorter RNAs with fewer exons promote ZFC3H1 "opening" and exosomal degradation, while longer RNAs favor nuclear export.

Conclusions:

• ZFC3H1's activity is decoupled from its initial loading, allowing for dynamic regulation of RNA fate.
• RNA features, specifically length and exon count, act as crucial determinants for switching between degradation and export pathways.
• This mechanism ensures efficient clearance of aberrant or short RNAs while permitting the export of functional mRNAs.