Christopher Bakkenist, PhD

Higher eukaryotes evolved with mechanisms that initiate DNA replication at multiple origins on multiple chromosomes in a pattern that is broadly conserved from one cell division to the next.  Multiple origins are needed as the replication of human chromosome 1 from a single origin would take 50 days.  The number of origins that can fire at a given time is limited, however, as cellular dNTP concentrations are 50-fold lower than that needed to replicate the genome. The mechanisms that determine when and where origins fire are not known.     

Activation of the replicative helicase is the first step in origin firing in eukaryotes.  Activation of the replicative helicase at a single origin in each of ~50,000 replicons is sufficient to replicate the human genome in the absence of stress.  These ~50,000 origins are selected from a tenfold excess of licensed origins.  Activation of additional replicative helicases at origins that would otherwise be passively replicated is observed after stress.  This plasticity in origin use is a simple mechanism to recover DNA replication between stalled replication forks.  The mechanisms that limit origin firing to one per replicon in the absence of stress are not known.

CD8 T cells divide 15 to 20 times in 7 days and a T cell can replicate its genome in less than 4 hours.  We are interested in the fundamental mechanisms that limit origin firing, how these mechanisms are alleviated to allow accelerated replication, and the impact of unrestricted DNA replication on genome stability and immune cell function.