Date

Tuesday 15 Sep 2026

Time

15:05 - 15:35

Location

BW031

Supervisor

Remus Dame

2nd reviewer

Rene Olsthoorn

Jury

Madeline Kavanagh

Chromatin organization is essential for genome compaction and gene regulation. While eukaryotes primarily use histones, prokaryotes rely mainly on nucleoid-associated proteins (NAPs) to organize their genomes. Asgard archaea, the closest prokaryotic relatives of the last eukaryotic common ancestor, can provide important insights into the evolution towards eukaryotic chromatin, yet their genome organization remains poorly understood. Alba proteins are archaeal NAPs that have been identified in most Asgard archaea, but their nucleic acid-binding properties and role in Asgard chromatin organization are largely unexplored. Here, we provide the first systematic characterization of Asgard Alba proteins, expanding on previous work describing the purification and initial characterization of Candidatus Lokiarchaeum ossiferum Alba. We optimized and established new expression and purification protocols for the Asgard Alba proteins of L. ossiferum and Promethearchaeota archaeon Loki b32, alongside the canonical Alba proteins of Sulfolobus Solfataricus for comparison. Using in vitro biophysical and biochemical approaches, we demonstrate that the investigated Asgard Alba proteins bind to both DNA and RNA without a discernible substrate preference, stiffen DNA in an F60-dependent manner, and exhibit lower thermostability than canonical Alba proteins. In addition, we found that the Alba protein of L. ossiferum can bridge DNA. Furthermore, we identify a previously uncharacterized Asgard-specific Alba cluster and show that one of its members forms protein mediated DNA-bridges and aggregate-like structures upon interaction with DNA. Collectively, our findings point to a broader functional diversity of Asgard Alba proteins and contribute to the understanding of Asgard chromatin organization, thereby advancing our knowledge of chromatin evolution and eukaryogenesis.