Human genes often contain segments known as introns that do not code for proteins.
To accurately express genetic instructions, cells must eliminate these introns.
Understanding how cells differentiate between coding and non-coding sequences is crucial for improving human health.
The minor spliceosome, a specialized molecular complex, is instrumental in this process.
When it malfunctions, it can lead to various genetic disorders.
Function of the Spliceosome
In human cells, only a small portion of the genetic blueprint within genes is used for protein production.
This selection process is facilitated by a complex assembly known as the spliceosome, which carefully separates coding regions from their non-coding counterparts.
The spliceosome is vital for proper cell function, and its dysfunction is linked to numerous genetic conditions.
Eukaryotic cells utilize two spliceosome types to edit genes: the well-studied major spliceosome and the less understood minor spliceosome.
A recent investigation led by the Galej Group at EMBL Grenoble has shed new light on the minor spliceosome, revealing its structure in research published in the journal Molecular Cell.
Structure of the Minor Spliceosome
While the major spliceosome has been the focus of intense scrutiny for over four decades, the minor spliceosome has largely remained in the shadows, despite its significant role in splicing.
The latest study outlines the structure of U11 snRNP, one of the five essential components of the minor spliceosome, which plays a key role in selecting introns for removal.
Spliceosomes operate as crucial editing machinery, removing non-coding segments, or introns, from messenger RNA precursors (pre-mRNA).
These molecules serve as messengers, conveying genetic material from DNA to protein.
By splicing, the spliceosomes clarify the fragmented messages within pre-mRNA.
Most genes contain numerous major introns, which are spliced out by the major spliceosome.
In contrast, a small fraction—about 0.5%—of genes consists of minor introns, which the minor spliceosome handles.
One postdoctoral fellow from the Galej Group emphasized that even though minor introns are rare, they hold significant importance, frequently residing within housekeeping genes that are vital for survival.
Understanding the Evolution of Spliceosomes
The spliceosome is a large, dynamic complex made up of RNA and proteins.
The major spliceosome comprises five subunits—U1, U2, U4, U6, and U5 small nuclear ribonucleoproteins (snRNPs)—along with approximately 150 associated proteins that facilitate various aspects of splicing.
The minor spliceosome has a similar arrangement but features distinct core components: U11, U12, U4atac, U6atac, and U5 snRNPs.
However, the precise configuration and functional roles of these components within the minor spliceosome remain largely enigmatic.
Studying large molecular machines like the spliceosome is challenging due to their inherently dynamic nature, especially for those that exist in only limited amounts, like the minor spliceosome.
One of the primary obstacles faced by the researchers was the selective purification of the minor spliceosome from whole cell extracts.
To overcome this challenge, researchers developed innovative biochemical techniques to isolate and analyze the minor spliceosome with higher specificity.
Recent breakthroughs, including dnananoparticle motors advancement, have provided new tools for manipulating and studying these complex molecular assemblies with unprecedented precision.
These advancements pave the way for deeper insights into the mechanisms governing RNA splicing and its regulatory processes.
At the project’s outset, the Galej Group discovered that knowledge of the minor spliceosome was sparse, with only a handful of teams investigating its structural properties.
Despite their evolutionary connection, it is believed that the last common ancestor of all eukaryotes already possessed both spliceosome types, diverging over 1.5 billion years ago—a timeline that is staggering to grasp.
The research team employed biochemical techniques alongside cryo-electron microscopy to unravel the structure of the U11 snRNP complex.
This process highlighted how U11 snRNP identifies the “5′ splice site,” the critical starting point for the removal of introns, triggering the splicing process.
The findings unveiled an intriguing structural difference between U11 snRNP and its major spliceosome relative, U1 snRNP.
This more complex architecture allows U11 snRNP to selectively recognize its rare substrates amidst the diverse RNA sequences found in cells.
Identifying the starting point for intron removal is just the first step in a complex assembly process.
Completing the splicing reaction entails navigating through a minimum of a dozen additional steps, yet the intricacies of how the minor spliceosome transitions through these intermediate stages remain poorly understood.
While this study marks a significant advancement in understanding the minor spliceosome, many questions linger.
The research provides valuable insights into the mechanisms behind minor intron selection, enriching our knowledge of the evolutionary trajectory of splicing machinery.
These findings pave the way for future inquiries into other minor spliceosome complexes, with the ultimate aim of comprehensively understanding this molecular pathway.
Such advancements could illuminate genetic disorders linked to minor spliceosome components and lead to innovative therapeutic strategies.
Source: ScienceDaily