Reconciling DNA replication and transcription in a hyphal organism: Spatial dynamics of transcription complexes in live Streptomyces coelicolor A3(2)

Abstract

Reconciling transcription and DNA replication in the growing hyphae of the filamentous bacterium Streptomyces presents several physical constraints on growth due to their apically extending and branching, multigenomic cells and chromosome replication being independent of cell division. Using a GFP translational fusion to the {beta}-subunit of RNA polymerase (rpoC-egfp), in its native chromosomal location, we observed growing Streptomyces hyphae using time-lapse microscopy throughout the lifecycle and under different growth conditions. The RpoC-eGFP fusion co-localised with DNA around 1.8 m behind the extending tip, whereas replisomes localise around 4-5 m behind the tip, indicating that at the growing tip, transcription and chromosome replication are to some degree spatially separated. Dual-labeled RpoC-egfp/DnaN-mCherry strains also indicate that there is limited co-localisation of transcription and chromosome replication at the extending hyphal tip. This likely facilitates the use of the same DNA molecule for active transcription and chromosome replication in growing cells, independent of cell division. This represents a novel, but hitherto unknown mechanism for reconciling two fundamental processes that utilise the same macromolecular template that allows for rapid growth without compromising chromosome replication in filamentous bacteria and may have implications for evolution of filamentous growth in microorganisms, where uncoupling of DNA replication from cell division is required.