Characterisation of ParH, a Novel Protein for Chromosome Organisation in the Filamentous Bacterium Streptomyces coelicolor

Abstract

The replication and segregation of chromosomes are essential processes during bacterial cell division to ensure that each new cell receives a complete set of chromosomes. Chromosome segregation in bacteria is often controlled by the ATP-ase ParA and the DNA binding protein ParB. The dynamic interaction between ParA and ParB governs movement and positioning of the chromosomal origin of replication (ori) within the cell. In the filamentous bacterium Streptomyces coelicolor, the ParAB proteins have been shown to control both chromosome organisation and septum placement during the synchronous cell division event of sporulation. Intriguingly, both ParA and ParB were shown to interact with proteins involved in polar growth. In addition to ParAB there are several ParA-like proteins in S .coelicolor that have not been fully characterised. One of these proteins, designated ParH, has 49% identity to Soj and 30% identity to MinD of Bacillus subtilis. The ParH is presumably co-translated with the downstream gene, which encodes a small hypothetical protein (Hyp). Through bioinformatic analysis, homologues of ParH and Hyp were found in numerous Actinobacteria. The knockout mutant of parH shows delayed sporulation and irregularities in septum placement suggesting that ParH might also contribute to correct chromosome organisation in Streptomyces. In this work, we were building on preliminary in vivo data generated previously in our lab. Our aim was to complement the in vivo experiments with the in vitro characterisation of ParH and some of its interacting partners and to compare the gene expression pattern of the parH mutant compared to the wild type strain during morphological differentiation on solid media.