SMC Protein-Dependent Chromosome Condensation during Aerial Hyphal Development in Streptomyces

Abstract

Members of the SMC (structural maintenance of chromosomes) protein family play a central role in higher-order chromosome dynamics from bacteria to humans. So far, studies of bacterial SMC proteins have focused only on unicellular rod-shaped organisms that divide by binary fission. The conversion of multigenomic aerial hyphae of the mycelial organism Streptomyces coelicolor into chains of unigenomic spores requires the synchronous segregation of multiple chromosomes. Here we focus on the contribution of SMC proteins to sporulation-associated chromosome segregation in S. coelicolor. Deletion of the smc gene causes aberrant DNA condensation and missegregation of chromosomes (7.5% anucleate spores). In vegetative mycelium, immunostained SMC proteins were observed sporadically, while in aerial hyphae about to undergo sporulation they appeared as irregularly spaced foci which accompanied but did not colocalize with ParB complexes. Our data demonstrate that efficient chromosome segregation requires the joint action of SMC and ParB proteins. SMC proteins, similarly to ParAB and FtsZ, presumably belong to a larger group of proteins whose expression is highly induced in response to the requirement of aerial hyphal maturation.Higher-order chromosome structure is particularly critical in the segregation of replicated chromosomes during cell division in eubacteria, eukaryotes, and archaea. Recent studies have shown that members of the SMC (structural maintenance of chromosomes) protein family play a central role in higher-order chromosome dynamics, acting either as condensins or cohesins (15-17, 30, 32, 36, 40). SMC are large proteins (110 to 170 kDa) that form dimers. Their N-and C-terminal parts form a single head domain (see references 13, 15-17, and 38 for reviews). SMC proteins exhibit ATPase activity that is required for their dynamic interaction with DNA (17). The results of recent studies demonstrated that bacterial SMC protein functions in complexes with other proteins, i.e., ScpA and ScpB (Scp's are segregation and condensation proteins) (6,29,37).In contrast to eukaryotes, in eubacteria the cell-cycle events, including replication, condensation, and segregation, take place simultaneously (16,26). Thus, during the bacterial cell cycle, chromosomes must undergo dynamic changes. So far, studies regarding chromosome dynamics have focused on Bacillus subtilis, Caulobacter crescentus, and Escherichia coli. In these organisms, SMC proteins (or MukB, a functional homologue in E. coli) appear to play similar roles; they are involved in chromosome organization and segregation. The genes encoding these proteins are not essential, although their deletion results in temperature-sensitive growth (2,9,22,31,32,38). In B. subtilis, smc deletion mutants exhibit complex phenotypes under permissive conditions, including poorly compacted nucleoids and a relatively large amount of anucleate cells (up to 15% of the cells were anucleate) (10). Interestingly, the inactivation of smc enhances the chromosome segregation defect of spo0J-or...

Topoisomerase I (TopA) Is Recruited to ParB Complexes and Is Required for Proper Chromosome Organization during Streptomyces coelicolor Sporulation

“…S2 in the supplemental material). Interestingly, TopA depletion in the ⌬parB background (PS03) led to a decrease in chromosome segregation abnormalities (8.9% anucleate prespores) compared to that in the parB deletion strain (J3305, with 19.5% anucleate prespores) (21). This may indicate that increased DNA compaction may partially rescue the chromosome segregation defect observed in the parB deletion strain.…”

“…In Streptomyces, as in other bacteria, additional proteins (e.g., SMC proteins and FtsK) contribute to efficient chromosome segregation (21,22,43). SMC proteins condense the nucleoids in the forming prespores, and analysis of an smc deletion strain suggested that this chromosome compaction is required for efficient segregation (21,22). Since Streptomyces chromosomes are linear, the requirement for decatenase activity during their segregation is not obvious.…”

“…Plasmid pET28topA was used to reclone the topA gene (3,372 bp, without the promoter) digested with NdeI and EcoRI into the similarly digested integrative plasmid pIJ6902 (containing the inducible P tipA promoter). The obtained pIJ6902topA plasmid was introduced into S. coelicolor strains M145 (wild type), J3310 (expressing parB-egfp) (41), and J3305 (⌬parB), yielding strains PS07, PS09, and PS08, respectively (21). The native topA gene was then deleted from the obtained strains using PCR targeting (50).…”

“…Before septation, the ParB complexes become uniformly aligned along the aerial hyphae via an interaction with ParA polymers (42). In Streptomyces, as in other bacteria, additional proteins (e.g., SMC proteins and FtsK) contribute to efficient chromosome segregation (21,22,43). SMC proteins condense the nucleoids in the forming prespores, and analysis of an smc deletion strain suggested that this chromosome compaction is required for efficient segregation (21,22).…”

“…The proteins that influence chromosome segregation and spatial organization include condensins: proteins of the structural maintenance of chromosomes (SMC) (in B. subtilis, S. coelicolor, Streptococcus pneumoniae, and Staphylococcus aureus) or MukB (in E. coli) families, which generate large-scale compaction of the chromosome (17)(18)(19)(20)(21)(22)(23)(24). Interestingly, the SMC proteins have been shown to be recruited to ParB complexes in B. subtilis and S. pneumoniae, confirming the importance of oriC region compaction for chromosome segregation (25,26).…”