Prokaryotes organise their DNA with nucleoid associated proteins like eukaryotes use histones. A bacterial chromosome is typically 1000 times the length of the cell and therefore, like eukaryotes, prokaryotes must dramatically compact their chromosomes. However, sections of DNA must be unpackaged readily to allow replication and transcription, especially in adapting environments. Nucleoid associated proteins, such as the histone-like protein, HU (a DNA binding protein), play important roles in the compaction of the bacterial nucleoid, regulation of genes, and the initiation of DNA replication. However, how the chromosome is remodelled in bacterial pathogens upon infection to allow rapid gene expression and adaptation is poorly understood.
This is especially true for the drug-resistant, sexually transmitted bacterium Neisseria gonorrhoeae (gonococcus). The gonococcus is a master of survival. It can colonise and survive within epithelial cells of the human urogenital tract despite the low pH and can survive inside highly toxic neutrophils, requiring rapid chromosome remodelling for gene expression and adaptation to combat imminent cell death. Additionally, the gonococcus is polyploid with up to three copies of the chromosome per cell.
Here we are investigating the role of the nucleoid associated protein HU to gain insights into how the architecture of N. gonorrhoeae chromosomes change upon infection and how changes in chromosome organisation allow the gonococcus to rapidly alter gene expression.
Deletion of hu from the gonococcal chromosome results in a decreased growth rate, suggesting that HU is important for chromosome stability during active growth and DNA replication. Exposure of wild-type MS11 and hu deletion strains to DNA damage indicates HU is also important for the DNA repair process, with notable survival differences in the deletion strain. In vitro DNA binding assays validate binding of HU to nicked DNA, intact DNA and damaged DNA, confirming the important role of HU in the gonococcus. Future work includes RNA-Seq to determine how HU affects gene expression, which we will pair with ChIP-Seq approaches alongside high resolution microscopy experiments to visualise chromosome compaction in the presence and absence of HU. Collectively this will determine the role of HU in chromosome maintenance and gene expression in the gonococcus.