Exonok

Exonok is a hypothetical regulatory protein used in educational contexts to illustrate exon recognition during pre-mRNA splicing. It is a fictional model and has no experimental evidence or known natural orthologs.

The name Exonok combines the word exon with a pedagogical suffix, signaling its role in exon inclusion within the teaching scenario. The term is used primarily in textbooks and classroom discussions to help explain how splicing factors influence whether an exon is retained or skipped.

In common teaching depictions, Exonok is portrayed as a modular protein with two RNA recognition motif (RRM) domains, a flexible linker, and a C-terminal coiled-coil domain that mediates dimerization. It is imagined to localize to the cell nucleus and to concentrate in nuclear speckles in illustrative models.

Mechanism, as presented in educational materials, involves Exonok binding to exonic splicing enhancers (ESEs) via its RRMs. Through interactions with serine/arginine-rich (SR) proteins and other core spliceosome components, Exonok is shown to act as a scaffold that stabilizes the assembly of the spliceosome at nearby splice sites, thereby promoting exon inclusion in the mature transcript.

Usage and significance: Exonok serves as a teaching tool to demonstrate how the strength of enhancers, protein–protein interactions, and dimerization can influence splicing outcomes. It also provides a simplified framework for exploring how computational models predict exon inclusion.

Limitations: Exonok is a conceptual construct and not observed in experiments. Real splicing involves many factors and regulatory layers beyond this simplified model.