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

Candidate partitioning genes (parA andparB ) for the linear chromosome ofStreptomyces coelicolor were identified by DNA sequencing in a series of seven genes located betweenrnpA andtrxA near the chromosomal replication origin. The most likely translation start point ofparB overlapped theparA stop codon, suggestive of coregulation, and transcription analysis suggested that the two genes formed an operon. Deletion of part ofparB 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 bothparA andparB . Reinforcing the idea of a special role for thepar locus during sporulation, the stronger of twoparAB promoters was greatly upregulated at about the time when sporulation septation was maximal in colonies. Three copies of a 14-bp inverted repeat (GTTTCACGTGAAAC) were found in or near theparAB genes, and at least 12 more identical copies were identified within 100 kb oforiC 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 fromBacillus subtilis believed to be important for DNA partitioning (D. C.-H. Lin and A. D. Grossman, Cell 92:675–685, 1998). One of these sites encompassed the transcription start point of the strongerparA promoter.