RESUMO
Bacterial chromosomes (though not Escherichia coli and some other gamma-proteobacterial chromosomes) contain parS sequences and parAB genes encoding partitioning proteins, i.e. ParA (ATPase) and ParB (DNA-binding proteins) that are components of the segregation machinery. Here, mycobacterial parABS elements were characterized for the first time. parAB genes are not essential in Mycobacterium smegmatis; however, elimination or overexpression of ParB protein causes growth inhibition. Deletion of parB also leads to a rather severe chromosome segregation defect: up to 10% of the cells were anucleate. Mycobacterial ParB protein uses three oriC-proximal parS sequences as targets to organize the origin region into a compact nucleoprotein complex. Formation of such a complex involves ParB-ParB interactions and is assisted by ParA protein.
Assuntos
Proteínas de Bactérias/metabolismo , Segregação de Cromossomos , Cromossomos Bacterianos/genética , Proteínas de Ligação a DNA/metabolismo , Mycobacterium smegmatis/genética , Adenosina Trifosfatases/genética , Adenosina Trifosfatases/metabolismo , Proteínas de Bactérias/química , Proteínas de Bactérias/genética , Sequência de Bases , Meios de Cultura , Proteínas de Ligação a DNA/química , Proteínas de Ligação a DNA/genética , Deleção de Genes , Regulação Bacteriana da Expressão Gênica , Dados de Sequência Molecular , Mycobacterium smegmatis/crescimento & desenvolvimento , Mycobacterium smegmatis/metabolismo , Mycobacterium tuberculosis/genética , Mycobacterium tuberculosis/metabolismo , Óperon , Proteínas Recombinantes de Fusão/genética , Proteínas Recombinantes de Fusão/metabolismo , Origem de ReplicaçãoRESUMO
The dynamic, mitosis-like segregation of bacterial chromosomes and plasmids often involves proteins of the ParA (ATPase) and ParB (DNA-binding protein) families. The conversion of multigenomic aerial hyphae of the mycelial organism Streptomyces coelicolor into chains of unigenomic spores requires the synchronous segregation of multiple chromosomes, providing an unusual context for chromosome segregation. Correct spatial organization of the oriC-proximal region prior to septum formation is achieved by the assembly of ParB into segregation complexes (Jakimowicz et al., 2005; J Bacteriol 187: 3572-3580). Here, we focus on the contribution of ParA to sporulation-associated chromosome segregation. Elimination of ParA strongly affects not only chromosome segregation but also septation. In wild type hyphae about to undergo sporulation, immunostained ParA was observed as a stretched double-helical filament, which accompanies the formation of ParB foci. We show that ParA mediates efficient assembly of ParB complexes in vivo and in vitro, and that ATP binding is crucial for ParA dimerization and interaction with ParB but not for ParA localization in vivo. We suggest that S. coelicolor ParA provides scaffolding for proper distribution of ParB complexes and consequently controls synchronized segregation of several dozens of chromosomes, possibly mediating a segregation and septation checkpoint.