Alba shapes the archaeal genome using a delicate balance of bridging and stiffening the DNA

Architectural proteins have an important role in shaping the genome and act as global regulators of gene expression. How these proteins jointly modulate genome plasticity is largely unknown. In archaea, one of the most abundant proteins, Alba, is considered to have a key role in organizing the genome. Here we characterize the multimodal architectural properties and interplay of the Alba1 and Alba2 proteins using single-molecule imaging and manipulation techniques. We demonstrate that the two paralogues can bridge and rigidify DNA and that the interplay between the two proteins influences the balance between these effects. Our data yield a structural model that explains the multimodal behaviour of Alba proteins and its impact on genome folding. How the genome is physically organized is less understood in archaea than in eubacteria or eukaryotes. Laurens et al. measure DNA binding by the Sulfolobus solfataricus proteins Alba1 and Alba2 using single-molecule techniques and conclude that the presence of Alba2 leads to more bridging between DNA.