Andreas Kegel's Group

Our group at the Department of Cell and Molecular Biology is studying the origin and functional properties of supercoiled DNA. In particular, we study the topological function of the evolutionarily conserved Smc5/6 complex using the advantage of the fruit fly Drosophila melanogaster and budding yeast Saccharomyces cerevisiae as model organisms.

Topological structures are frequently arising when the two complementary strands of the DNA double helix are unwound by helicases, which is crucial for cellular processes like DNA replication and transcription. However, unresolved topological tension may trigger aberrant chromosome functions that are the underlying cause of many developmental abnormalities and human diseases. Thus, to understand the biological role of supercoiled DNA with regard to development and disease formation we explore the molecular mechanisms resolving chromosomal entanglements. To address the importance of DNA topology and topological changes in DNA packaging, replication, transcription, and recombination we apply genetic tools and techniques to generate and investigate fly stocks and yeast strains with specific mutations. In addition, cytological studies on chromosomes including fluorescence microscopy analysis and other cellular imaging techniques are employed, as well as biochemical techniques for protein extraction and protein analysis by immunoblotting and protein-protein interaction assays.

Figure: Smc5/6 sequesters pre-catenanes behind the fork and thereby facilitates fork rotation. During the process of DNA replication the two complementary strands of the double helix are unwound by helicases. Since helicases only separate but do not unwind the two strands, movement of the fork results in acute overwinding (positive supercoiling) ahead of the tracking system. A unique class of enzymes called topoisomerases (Top1/Top2) resolves the topological tension of DNA by generating transient breaks in the double helix without changing the primary structure. An alternative strategy to avoid accumulation of supercoiled DNA ahead of the fork is based on a hypothesis that allows the advancing fork to rotate with the turn of the helix. Fork rotation will lead to pre-catenane formation behind the replication fork, which are sequestered by Smc5/6 and efficiently removed by Top2 before entry into mitosis.

Group Members

Andreas Kegel Senior lab manager
Ingrid Lilienthal Doctoral student 

Selected publications

Chromosome length influences replication-induced topological stress.
Kegel A, Betts-Lindroos H, Kanno T, Jeppsson K, Ström L, Katou Y, et al
Nature 2011 Mar;471(7338):392-6

Genome wide distribution of illegitimate recombination events in Kluyveromyces lactis.
Kegel A, Martinez P, Carter S, Aström S
Nucleic Acids Res. 2006 ;34(5):1633-45

Functional diversity of silencers in budding yeasts.
Sjöstrand J, Kegel A, Aström S
Eukaryotic Cell 2002 Aug;1(4):548-57

Nej1p, a cell type-specific regulator of nonhomologous end joining in yeast.
Kegel A, Sjöstrand J, Aström S
Curr. Biol. 2001 Oct;11(20):1611-7

The Smc5/6 complex: more than repair?
Kegel A, Sjögren C
Cold Spring Harb. Symp. Quant. Biol. 2010 ;75():179-87

Cell Biology