RNA-binding proteins are highly important in regulating gene expression.
In eukaryotic cells, RNA-binding proteins are involved in the spliceosome, allowing the removal of introns. This is through the use of Snurps, or small nucleolar riboproteins. By binding specifically to the pre-mRNA / hnRNA, they identify the start and end of introns (U1, U2) and bring these sites together to catalyse the formation of a lariat (U4, U5, U6). This process is also involved in alternative splicing, allowing the formation of protein isoforms. This is beneficial as it increases the size of an organism’s proteome without making its genome larger.
RNA-binding proteins can also bind to motifs on mRNAs, inhibiting protein synthesis. This is a post-translational modification that is able to suppress gene expression, and can be exploited for therapeutic uses.
These proteins can also be used for protein localisation. By attaching a protein to mRNA transcripts, they can be localised to desired regions - which is important during early embryonic development. An example of this is bicoid and nanos in Drosophila. This enables the development of the anterior-posterior axis, which is important for the correct development of the fly.
Poly(A) binding protein (PABP) is another RNA-binding protein that is important. The poly(A) tail in the untranslated region (UTR) of an mRNA transcript allows PABP to bind. PABP is important in post-transcriptional control of protein synthesis, ensuring that a complex transcript is formed. If there is a premature STOP codon, nonsense mediated decay can be initiated due to the absence of PABP from the end of the coding region. Poly(A) tail decay reduces the binding area for PABP, eventually making it impossible to bind and thus the mRNA is degraded. These both allow post-transcriptional control of gene expression, by mediating protein synthesis.