Partitioning of the Linear Chromosome during Sporulation of Streptomyces coelicolor A3(2) Involves an oriC -Linked parAB Locus

Abstract

Candidate partitioning genes (parA and parB) for the linear chromosome of Streptomyces coelicolor were identified by DNA sequencing in a series of seven genes located between rnpA and trxA near the chromosomal replication origin. The most likely translation start point of parB overlapped the parA stop codon, suggestive of coregulation, and transcription analysis suggested that the two genes formed an operon. Deletion of part of parB had no effect on the growth or appearance of colonies but caused a deficiency in DNA partitioning during the multiple septation events involved in converting aerial hyphae into long chains of spores. At least 13% of spore compartments failed to inherit the normal DNA allocation. The same phenotype was obtained with a deletion removing a segment of DNA from both parA and parB. Reinforcing the idea of a special role for the par locus during sporulation, the stronger of two parAB promoters was greatly upregulated at about the time when sporulation septation was maximal in colonies. Three copies of a 14-bp inverted repeat (GTTTCACGT GAAAC) were found in or near the parAB genes, and at least 12 more identical copies were identified within 100 kb of oriC from the growing genome sequence database. Only one perfect copy of the 14-bp sequence was present in approximately 5 Mb of sequence available from the rest of the genome. The 14-bp sequence was similar to sequences identified as binding sites for Spo0J, a ParB homologue from Bacillus subtilis believed to be important for DNA partitioning

The bacterial nucleoid: A highly organized and dynamic structure

“…At present, their exact function is still unclear. It was, however, demonstrated that ParB interacts with conserved binding sites which are clustered in the origin-proximal region Easter and Gober, 2002;Bartosik et al, 2004] and that both proteins are necessary for proper chromosome segregation [Glaser et al, 1997;Mohl and Gober, 1997;Marston and Errington, 1999;Kim et al, 2000;Lewis et al, 2002]. With the exception of C. crescentus, however, deletion of parA or parB is not lethal and only results in mild growth phenotypes, which might imply redundancy in the systems that control positioning of the chromosome.…”

Towards understanding the molecular basis of bacterial DNA segregation

“…During vegetative growth, deletion of the parAB genes of Pseudomonas putida slightly increases the formation of anucleate cells, but during both the transition from exponential to stationary growth conditions and during overexpression of parAB, high levels of anucleate cells were formed (Godfrin-Estevenon et al 2002). Deletion of parAB in Streptomyces coelicolor had no detectable effect in vegetatively growing cells, but also resulted in the production of significant numbers of anucleate spores (Kim et al 2000).…”

Independent Segregation of the Two Arms of theEscherichia coli oriRegion Requires neither RNA Synthesis nor MreB Dynamics

“…ParA is an ATPase that binds ParB and is proposed to direct the ParB/parS complex to the poles (18). These partitioning systems serve to facilitate chromosome segregation but are often not essential, for example, in B. subtilis, Streptomyces coelicolor, and Pseudomonas putida and for V. cholerae chromosome I (18,23,30,35).In contrast, these systems are essential for viability in C. crescentus (41,54) and for segregation of chromosome II in V. cholerae (63). The latter requirement may be due to the fact that chromosome II has many properties of a large plasmid and its Par proteins are more closely related to plasmid-encoded ones than to those encoded on chromosomes (22).…”

“…ParA is an ATPase that binds ParB and is proposed to direct the ParB/parS complex to the poles (18). These partitioning systems serve to facilitate chromosome segregation but are often not essential, for example, in B. subtilis, Streptomyces coelicolor, and Pseudomonas putida and for V. cholerae chromosome I (18,23,30,35).…”