Control of Sporulation Gene Expression in Bacillus subtilis by the Chromosome Partitioning Proteins Soj (ParA) and Spo0J (ParB)

Abstract

Two chromosome partitioning proteins, Soj (ParA) and Spo0J (ParB), regulate the initiation of sporulation in Bacillus subtilis. In a spo0J null mutant, sporulation is inhibited by the action of Soj. Soj negatively regulates expression of several sporulation genes by binding to the promoter regions and inhibiting transcription. All of the genes known to be inhibited by Soj are also activated by the phosphorylated form of the transcription factor Spo0A (Spo0AϳP). We found that, in a spo0J null mutant, Soj affected sporulation, in part, by decreasing the level of Spo0A protein. Soj negatively regulated transcription of spo0A and associated with the spo0A promoter region in vivo. Expression of spo0A from a heterologous promoter in a spo0J null mutant restored Spo0A levels and partly bypassed the sporulation and gene expression defects. Soj did not appear to significantly affect phosphorylation of Spo0A. Thus, in the absence of Spo0J, Soj inhibits sporulation and sporulation gene expression by inhibiting accumulation of the activator protein Spo0A and by acting downstream of Spo0A to inhibit gene expression directly.Bacillus subtilis can sporulate in response to starvation and high cell density. Sporulation involves an asymmetric cell division and requires DNA replication and chromosome segregation. Spo0A is a critical transcription factor in early sporulation. Cells initiate sporulation when they accumulate a threshold amount of phosphorylated Spo0A (Spo0AϳP) (3,6,12). Many signals that regulate sporulation do so by affecting the accumulation of Spo0AϳP. Spo0A obtains phosphate from a set of proteins called the phosphorelay (2). A balance of kinases and phosphatases regulates phosphate input into the phosphorelay and the phosphorylation state of Spo0A (3,(30)(31)(32).Two proteins involved in chromosome partitioning, Soj and Spo0J, also regulate the initiation of sporulation, perhaps in response to chromosome structure or partitioning (4,14,28). Soj and Spo0J are members of the ParA-SopA and ParB-SopB protein families, respectively. Many ParA-and ParB-type proteins are encoded on low-copy-number plasmids and are required for accurate plasmid partitioning (29, 42). Chromosome-encoded family members have also been identified, several of which function in chromosome partitioning (14,22,26). Members of the ParA-SopA families can act as transcriptional repressors and are themselves often regulated by members of the ParB-SopB family (7,9,24,27,36).Spo0J is required both for accurate chromosome partitioning and for sporulation (14). Spo0J binds to a series of sites (parS sites) in the origin-proximal 20% of the chromosome (22), clustering them into a large focus (10,21,23). Defects in spo0J perturb chromosome partitioning. Cultures of spo0J null mutant cells produce approximately 1% anucleate cells, a frequency approximately 20-to 100-fold greater than that of wildtype cells (14).A null mutation in spo0J also causes an approximately 300-fold defect in sporulation relative to wild-type cells (14,28,34). spo0J null mutants ar...

Towards understanding the molecular basis of bacterial DNA segregation

“…Soj and other ParA proteins are members of a large family of ATPases that include the bacterial cell division regulator MinD, nitrogenase iron protein involved in biological nitrogen fixation and the anion pump, ATPase ArsA (Koonin 1993). Soj has been shown to associate with the promoter regions to inhibit the transcription of several early sporulation genes in vivo, an effect that is antagonized by Spo0J (Ireton et al 1994;Quisel & Grossman 2000;Quisel et al 1999). It is also known to play a role in the formation of condensed Spo0J focuses on oriC/parS (Marston & Errington 1999).…”

“…Mutations in the nucleotide binding site of Soj disrupt localization and function, rendering it insensitive to regulation by Spo0J (Quisel & Grossman 2000;Quisel et al 1999). These observations suggest that the non-oscillating form of Soj directs repression of early sporulation gene promoters and that the oscillating form does not.…”

Compartmentalization of Gene Expression duringBacillus subtilisSpore Formation

“…Spo0J colocalizes to cell poles with the chromosomal origin of replication (175), binds to sites near the chromosomal origin (174), and is required for optimal efficiency of chromosome segregation (130). In the absence of Spo0J, Soj binds to the promoter regions of at least four Spo0A-responsive genes (spo0A, spoIIA, spoIIE, and spoIIG) and represses their transcription (33,191,237,238). This effect appears to be mediated by dynamic protein localization; when Spo0J is present, Soj oscillates between sites near the poles of the cell, presumably preventing stable DNA-protein interaction and transcriptional repression.…”

The extrusion-capture model for chromosome partitioning in bacteria

“…The B. subtilis ParA and ParB homologs were first identified for their regulatory role during initiation of sporulation, a fact that is reflected in their names, Soj and Spo0J (Piggot and Coote 1976;Ireton et al 1994;Quisel et al 1999;Quisel and Grossman 2000). Spo0J (ParB) binds to at least eight parS sites located in the origin proximal 20% of the chromosome .…”