Biology subjects

Olafsson, G.

Publications and source records attributed to Olafsson, G..

3 recordsLinked to original sources

bioRxiv2023

Human macroH2A1 drives nucleosome dephasing and genome instability in histone-humanized yeast

In addition to replicative histones, eukaryotic genomes encode a repertoire of non-replicative variant histones providing additional layers of structural and epigenetic regulation. Here, we systematically replaced individual replicative human histones with non-replicative human variant histones using a histone replacement system in yeast. Variants H2A.J, TsH2B, and H3.5 complemented for their respective replicative counterparts. However, macroH2A1 failed to complement and its expression was toxic in yeast, negatively interacting with native yeast histones and kinetochore genes. To isolate yeast with "macroH2A1 chromatin" we decoupled the effects of its macro and histone fold domains, which revealed that both domains sufficed to override native yeast nucleosome positioning. Furthermore, both modified constructs of macroH2A1 exhibited lower nucleosome occupancy that correlated with decreased short-range chromatin interactions (<20 Kb), disrupted centromeric clustering, and increased chromosome instability. While supporting viability, macroH2A1 dramatically alters chromatin organization in yeast, leading to genome instability and massive fitness defects.

genetics↗

bioRxiv2023

Synthetic cell-cycle regulation identifies Mif2CENP-C as a CDK phospho-target at the kinetochore.

Protein phosphorylation regulates multiple cellular processes including cell-cycle progression, which is driven by highly conserved cyclin-dependent kinases (CDKs). CDKs are controlled by the oscillating levels of activating cyclins and the activity peaks during mitosis to promote chromosome segregation. However, with some exceptions, we do not understand how the multitude of CDK-phosphorylated residues within the proteome drive cell-cycle progression nor which CDK phosphorylation events are necessary. To identify yeast proteins whose phospho-regulation is most critical for cell-cycle progression, we created a synthetic CDK complex and systematically recruited this to proteins involved in chromosome segregation using the Synthetic Physical Interactions (SPI) method. We found that targeted recruitment of synthetic CDK to the centromeric protein Mif2CENP-C leads to enrichment of Mif2CENP-C at centromeres and arrested cells in late mitosis. We then identified putative CDK consensus sites on Mif2CENP-C which aid Mif2CENP-C localisation at centromeres and showed that CDK- dependent Mif2CENP-C phosphorylation is important for its stable kinetochore localisation. SummaryTo identify cellular sites of functional cell cycle phospho-regulation we generated a synthetic cyclin-dependent kinase which can be recruited to any given GFP-tagged protein. Using this system with a set of proteins involved in chromosome segregation, we identified Mif2CENP-C as a kinetochore target of CDK and show that CDK stabilises Mif2s kinetochore localisation.

cell biology↗

bioRxiv2022

DASH/Dam1 complex mutants stabilize ploidy by weakening kinetochore-microtubule attachments

Forcing budding yeast to chromatinize their DNA with human histones manifests an abrupt fitness cost. We previously proposed chromosomal aneuploidy and missense mutations as two potential modes of adaptation to histone humanization. Here we show that aneuploidy in histone-humanized yeasts is specific to a subset of chromosomes, defined by their centromeric evolutionary origins, however, they are not adaptive. Instead we show that a set of missense mutations in outer kineto-chore proteins drive adaptation to human histones. Further, we characterize the molecular mechanism of two mutants of the outer kinetochore DASH/Dam1 complex, which reduce aneuploidy by suppression of chromosome instability. Molecular modeling and biochemical experiments show that these two mutants likely disrupt a conserved oligomerization interface thereby weakening microtubule attachments. Lastly, we show that one mutant, DAD1E50D, while suppressing chromosome instability in mitosis, leads to gross defects in meiosis. In sum, our data show how a set of point mutations evolved in the histone-humanized yeasts to counterbalance human histone induced chromosomal instability through weakening microtubule interactions, eventually promoting a return to euploidy.

genetics↗