subtilis and Escherichia coli; however, the precise manner of SpoIISA toxicity remains unknown. In this work, we focused on the N-terminal, transmembrane domain of SpoIISA and verified the prediction of its topology. Using truncated SpoIISA constructs, we show that the entire transmembrane domain is required for its toxicity. Moreover, we propose that
the oligomerization of this transmembrane domain is crucial for activity of SpoIISA, possibly by forming a pore-like structure. “
“The pHW126-like plasmids are a recently discovered small group of cryptic plasmids replicating by the rolling circle mode. The replication origin of pHW126 consists of a conserved stretch, four perfect Avasimibe order direct repeats and a so-called accessory region. The latter increases plasmid stability but is not absolutely necessary for replication. Here, we report that
deletion of the accessory region causes rapid multimerization of pHW126. While the number RO4929097 of pHW126-units per cell remains constant, the number of physically independent plasmid molecules is reduced by approximately 40%, rendering random distribution to daughter cells less effective. A conserved inverted repeat within the accessory region could be identified as a sequence necessary for maintaining pHW126 in its monomeric form. A mutant version of pHW126 lacking this inverted repeat could be rescued by placing the single-strand initiation site (ssi) of pHW15 on the plus strand, while including the ssi in the opposite direction had no effect. Thus, our data provide evidence that multimer formation is, besides copy number
reduction and ssDNA accumulation, an additional means how loss of a mechanism ensuring efficient lagging strand synthesis may cause destabilization of rolling circle plasmids. Plasmids of bacteria appear in a wide variety of sizes, have different Sulfite dehydrogenase copy numbers and may encode various functions. Accordingly, plasmids have evolved different strategies for their maintenance. Huge circular plasmids usually replicate by the theta mechanism, are frequently self-transmissible and have a low copy number of just a few molecules per cell. Consequently, these plasmids depend on systems mediating partitioning, multimer resolution and postsegregational killing to ensure distribution to daughter cells. Small plasmids may also use the theta mode, but many of them replicate by the rolling circle mechanism or by strand displacement (del Solar et al., 1998; Rawlings & Tietze, 2001; Khan, 2005). Small plasmids are nonself-transmissible but may possess systems mediating mobilization in the presence of a conjugative plasmid (Francia et al., 2004; Garcillan-Barcia et al., 2009). Owing to their high copy number, small plasmids can rely on random distribution.
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