Neighboring inteins interfere with one another's homing capacity

Area of Science:

• Molecular Biology
• Genetics
• Microbiology

Background:

• Inteins are mobile genetic elements found across life, capable of invading host genes.
• The minichromosome maintenance (MCM) protein, crucial for DNA replication, presents multiple intein insertion sites in Haloarchaea.
• Specific intein insertion sites (MCM-a and MCM-d) are frequently targeted within the MCM protein.

Purpose of the Study:

• To investigate intein invasion dynamics and interactions between adjacent inteins in the MCM protein of *Haloferax mediterranei*.
• To analyze the frequency and conservation of intein insertion sites in MCM homologs across the Haloferacales order.
• To understand the mechanisms governing intein homing and splicing in haloarchaeal MCM proteins.

Main Methods:

• In vivo studies in *Haloferax mediterranei* to observe intein invasion and splicing.
• Computational analysis of MCM homologs from 129 Haloferacales species.
• Assessing intein recognition, cleavage, and homing efficiency under different invasion scenarios.

Main Results:

• Inteins at MCM-a and MCM-d sites are recognized and cleave their targets.
• Single intein homing is efficient, but co-homing into intein-free sites is less effective.
• Invasion is more successful when one intein is already present at a neighboring site.
• A specific amino acid substitution (Proline for Serine) at the MCM-d site prevents splicing but not recognition.

Conclusions:

• Intein invasion and homing in haloarchaeal MCM proteins exhibit complex dynamics, influenced by the presence of neighboring inteins.
• The efficiency of intein homing is context-dependent, favoring invasion of already partially invaded alleles.
• Specific extein residues can modulate intein splicing without abolishing intein recognition, highlighting intricate host-intein interactions.