Regulated Chromatin Assembly at Replication Origins

• Applicant: Dr. Christoph Kurat
• Subject Area: General Genetics and Functional Genome Biology
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 554463232

The replication of genomic DNA before cell division represents a fundamental process in the life cycle of a cell. Errors in this mechanism can have severe consequences for a cell, including DNA damage, which is a hallmark of cancer. It is therefore of the utmost importance to meticulously regulate DNA replication in order to ensure its accuracy and timely execution within the cell's lifecycle. DNA replication is a two-phase process. In the G1 phase of the cell cycle, the origin-recognition complex (ORC), assisted by a number of factors and adenosine triphosphate (ATP), loads two minichromosome maintenance (MCM) complexes onto the replication origins. This pivotal stage is designated as 'origin licensing'. The helicase remains inactive during the G1 phase and becomes active only in the subsequent S phase. A complex array of replication factors, in conjunction with two key cell cycle kinases, Cyclin-Dependent Kinase (CDK) and Dbf4-Dependent Kinase (DDK), facilitate the transformation of the dormant MCM complex into an active helicase. This activation marks the commencement of DNA replication, which is designated as 'origin firing'. Given the considerable size of genomes, replication initiation must occur at multiple origins. For instance, the yeast Saccharomyces cerevisiae utilises approximately 300 confirmed core origins to replicate its 12-megabase pair genome. Conversely, it is postulated that human cells necessitate approximately 30,000 origins for genome replication. Although we have a comprehensive understanding of the basic replication process, the majority of biochemical and structural studies have focused on the 'naked system', which refers to just the replication process on DNA without any other associated proteins. However, eukaryotic replisomes interact with histone-bound DNA, which is packaged as nucleosomes, the fundamental units of chromatin. The intrinsic stability of nucleosomes presents a challenge to replication processes, as they can impede the progression of replication due to their inherent stability. Nevertheless, chromatin also plays an important regulatory role, for example, in transcription. In contrast to the intricate interplay between transcription and chromatin, the mechanisms by which replication deals with nucleosomes during genome replication remain poorly understood. This represents the next major level in replication research that we must now address.

• DFG Programme: Research Grants