Examining the mechanism of chromatin replication and assembly at telomeres

Each human telomere is composed of 10-15 kb of repetitive DNA bound by a protein complex called shelterin, which forms a protective nucleoprotein cap at the chromosome end. In addition to shelterin, telomeric DNA is also wrapped around histone octamers in a closed, heterochromatic state that compacts telomeric DNA and represses transcription at the chromosome end (Tardat and Dejardin, 2018).

Mutations that disrupt the assembly of chromatin at telomeres cause DNA damage and are found in essentially all 'ALT' type cancer cells (some 10-15 % of all tumour types), underlining the importance of chromatin in the function of telomeres. At non-telomeric sites, chromatin is assembled during S-phase when chromatin remodelling factors and histone chaperones disassemble nucleosomes in front of the replication fork and reassemble them on newly synthesised DNA (Hoek and Stillman, 2003).

Although telomeric chromatin is also assembled during S-phase, genetic studies show that a distinct set of chromatin remodelling factors are required for this process, suggesting the replication and reassembly of nucleosomes at telomeres occurs through a distinct mechanism. The successful candidate will examine this mechanism using a combination of reconstitution biochemistry, biophysics and genetics. The starting point for the project is a reconstituted system for DNA replication that we have

recently developed in the Telomere Biology lab. Combining this system with chromatinised DNA templates and purified chromatin remodelling factors, we will examine i) how chromatin affects the human replication fork ii) how telomere-specific chromatin remodelling factors allow replication and reassembly of nucleosomes on telomeric DNA and iii) the consequences of disrupting these processes within cells.

As opportunities arise, we will also collaborate with other groups to characterise replication intermediates using cutting edge biophysical and structural techniq