Bayer School of Natural and Environmental Sciences
chromosome segregation, ftsk, Streptomyces, DNA translocase, development, condensation, chromosome architecture
A quintessential phenomenon occurring during prokaryotic development is accurate segregation of the replicated genomes into the daughter cells. Key energy-dependent processes like chromosome condensation and subcellular partitioning of the genomes are driven by conserved proteins like SMC, ParB, FtsK. During its complex developmental cycle, Streptomyces coelicolor segregates its genomes into chains of unicellular spores when its multigenomic syncytial aerial hyphae undergo division.
A novel ftsK-like gene, hfkA (Homolog of FtsK protein A), was examined for function and localization during development-associated chromosome segregation. Individual deletions did not affect segregation, but a ΔhfkA ΔftsK mutant exhibited 8% anucleate spores, suggesting that HfkA and FtsK are redundant in function. To understand the combined effect of existing deletions, a series of mutant strains of hfkA, ftsK, smc and parB were isolated and analyzed. The triple mutants ΔhfkA ΔftsK Δsmc and ΔhfkA ΔftsK ΔparB indicated an additive property of the segregation defects of ΔhfkA ΔftsK with the Δsmc and ΔparB mutants, respectively. Finally, a viable quadruple hfkA ftsK smc parB strain was isolated with 20% anucleate spores, and showed no noticeable increase in its segregation phenotype from the double mutant ΔparB Δsmc (18.8%). This indicated that a complete deletion of hfkA and ftsK has no effect, whereas the loss of parB and smc causes the highest percentage of anucleate spores.
To collect additional data, a previously published ftsK’ truncated allele was tested. A ftsK’ smc parB triple mutant (10%) was used to isolate a hfkA ftsK’ smc parB quadruple mutant (14%). This strain did not have a severe phenotype compared to ΔftsK’ Δsmc ΔparB. It was lower in segregation defect than the quadruple mutant containing a complete deletion of ftsK, disproving that it was hfkA+ that was the reason ftsK’ had a lowering effect. It was concluded that ftsK’ and hfkA could be mitigating some of the segregation defect caused by the loss of parB smc.
Some FtsK/SpoIIIE-like proteins (Sco5734) have been characterized as type VII secretion system proteins in bacteria. Bioinformatics analysis suggests that HfkA could be a putative type VII membrane ATPase motor protein, which directly or indirectly affects segregation.
Sethi, S. (2019). Genetic analysis of a novel FtsK homolog, HfkA, in Streptomyces coelicolor development-associated chromosome segregation (Doctoral dissertation, Duquesne University). Retrieved from https://dsc.duq.edu/etd/1855