Universiteit Leiden

nl en


This Week’s Discoveries | 30 May 2017

30 mei 2017
Niels Bohrweg 2
2333 CA Leiden
De Sitterzaal

First lecture

How often does a Diophantine equation have a solution?

Efthymios Sofos (MI) is a postdoc in the Number Theory, Algebra and Geometry group at MI. His research interests lie in number theory, geometry and surrounding areas, focusing on Manin's conjecture on the distribution of rational points on surfaces and, more recently, on Serre's problem on the number of fibres of bounded height with a rational point.

Diophantine equations are polynomial equations in many variables, where every coefficient of the polynomial is an integer. Mathematicians since antiquity have been trying to find methods to answer whether solutions exist. In my talk I will focus on recent developments on the subject, namely describing how often certain families of equations have a solution or not.

Second lecture

The structure of chromatin; single-molecule experiments on model fibers and real genes

John van Noort (LION) is head of the Chromatin Dynamics group at LION. His group develops and uses modern biophysical techniques to unravel the physics behind DNA condensation. They are currently developing state-of-the-art single-molecule manipulation techniques, i.e. optical and magnetic tweezers, sp-FRET microscopy and video AFM, to allow for a rigorous biophysical characterization of the dynamics of these processes. John was appointed professor of Biophysics on 1 April.

The folding of DNA in chromatin defines access to our genes and therefore plays a pivotal role in transcription regulation. However, the structure of chromatin fibers is poorly defined and heavily debated. We use single-molecule techniques to probe and manipulate the dynamics of nucleosomes in individual chromatin fibers. These novel methods were initially applied to synthetic, highly homogeneous nucleosomal arrays and yielded unprecedented insight in the structure and dynamics of chromatin. Unfortunately, synthetic chromatin lacks the complexity that provides functionality to our epi-genome. We recently developed a method to purify specific chromatin fragments from yeast without chemical crosslinking of the fiber. I will show the first single-molecule force spectroscopy results on intact, native fibers which uniquely probe chromatin structure, composition and variations in it at the single-molecule level.