Modulation of the P1 Plasmid Partition Protein ParA by ATP, ADP, and P1 ParB

Abstract

ParA is an essential P1 plasmid partition protein. It represses transcription of the par genes (parA and parB) and is also required for a second, as yet undefined step in partition. ParA is a ParB-stimulated ATPase that binds to a specific DNA site in the par promoter region. ParA is an essential component of the P1 plasmid partition system (1). The prophage of bacteriophage P1 exists as an autonomously replicating plasmid, and its copy number is about the same as that of the bacterial chromosome (2). The P1 partition system, Par, directs proper segregation and thus stable maintenance of the plasmid. The mechanism of partition is unknown, but can be thought of as a positioning process that via interaction with the Escherichia coli host ensures proper distribution of the plasmid. Par encodes two essential transacting proteins, ParA and ParB, and contains a cis-acting DNA site called parS (1). In addition, the E. coli integration host factor, IHF, 1 also participates, although it is not absolutely required (3). ParB and IHF bind to parS to form the partition complex (3-5). Assembly of this complex is assumed to be an early step in the partition pathway. Formation of this complex does not require the action of ParA (3-5), and we infer that ParA acts during a later step in the partition process.ParA has at least two roles in partition. First, ParA represses transcription of its own gene and parB from a promoter upstream of parA (6). ParA repressor activity is stimulated by ParB; however, ParB has no effect on par gene expression on its own. A second role for ParA in partition is inferred from genetic data that show a requirement for ParA in partition even when its regulatory role is bypassed (6, 7). Therefore, we consider ParA's repressor activity its "regulatory" function, and this second, as yet undefined role as ParA's "partition" function because we think it reflects a direct role for ParA in the positioning reaction. The latter function requires that ParA interact, directly or indirectly, with the ParB-IHF-parS partition complex.ParA is an ATPase and a site-specific DNA-binding protein (8). The ATPase is stimulated by ParB and nonspecific DNA (8). ParA is one of the better characterized proteins in a superfamily of ATPases defined by a modified Walker type A motif in the protein sequence (9 -11). This superfamily includes other plasmid partition proteins such as F SopA, as well as plasmid and chromosomally encoded proteins from various bacteria species whose functions have not yet been determined (10 -12). Many of the plasmids and bacterial chromosomes also encode a ParB homolog adjacent to the ParA homolog. The similarities of these ParA-like proteins with P1 ParA and F SopA have led to the suggestion that these homologs are also involved in plasmid or chromosome segregation (10, 11).ParA binds to the par promoter region called parOP (8), and this binding is thought to mediate ParA repressor activity in vivo. The recognition site for ParA is likely a large inverted repeat in the par promoter region, since (i) ...

ParA2, aVibrio choleraechromosome partitioning protein, forms left-handed helical filaments on DNA

“…S1). The significance of this small difference is not known, but similar values have been reported for ParA of P1 and SopA of F (12,31,32).…”

Genome of Bacteriophage P1

“…Identification of putative 70 promoters was carried out using Targsearch (118). Putative Rho-independent transcriptional terminators were identified with the GCG program Terminator (40) and TIGR program TransTerm (85).…”

“…Regulatory regions of 38 operons contain one or more sequences that resemble strong 70 promoters (Table 4). Of 26 70 promoters identified previously by transcriptional fusion or primer extension experiments, only 9 had a match to the consensus sequence below 50% and required relaxing the stringency of the prediction program for their detection.…”

“…Of 26 70 promoters identified previously by transcriptional fusion or primer extension experiments, only 9 had a match to the consensus sequence below 50% and required relaxing the stringency of the prediction program for their detection. All nine S a A more complete table, which includes pI, number of amino acid residues (or nucleotides in RNA), and features of the amino acid sequence (closest homologs and amino acid sequence motifs) is to be found as Table S1 in the supplemental material.…”

Mapping of the interactions between partition proteins Delta and Omega of plasmid pSM19035 from Streptococcus pyogenes

“…The few detailed mutational studies of partition protein interactions concerned mainly type Ia systems (Walkertype ATPases with a DNA-binding function and ParB-like proteins with HTH DNA-binding motifs). ParB of Ia stimulates both the ATPase activity of ParA (Davey & Funnell, 1997) and the polymerization of ParA-like proteins Bouet et al, 2007;Machó n et al, 2007) crucial for separation of plasmid molecules. In the systems studied, it has been demonstrated that both proteins are able to interact with each other only in the dimeric form (Bouet & Funnell, 1999).…”