RESUMO
Although recent studies have provided a wealth of information about archaeal biology, nothing is known about the molecular basis of DNA segregation in these organisms. Here, we unveil the machinery and assembly mechanism of the archaeal Sulfolobus pNOB8 partition system. This system uses three proteins: ParA; an atypical ParB adaptor; and a centromere-binding component, AspA. AspA utilizes a spreading mechanism to create a DNA superhelix onto which ParB assembles. This supercomplex links to the ParA motor, which contains a bacteria-like Walker motif. The C domain of ParB harbors structural similarity to CenpA, which dictates eukaryotic segregation. Thus, this archaeal system combines bacteria-like and eukarya-like components, which suggests the possible conservation of DNA segregation principles across the three domains of life.
Assuntos
Proteínas Arqueais/química , Centrômero/química , Segregação de Cromossomos , Cromossomos de Archaea/genética , DNA Arqueal/genética , Sulfolobus/genética , Motivos de Aminoácidos , Proteínas Arqueais/genética , Autoantígenos/química , Autoantígenos/genética , Bactérias/genética , Centrômero/genética , Proteína Centromérica A , Proteínas Cromossômicas não Histona/química , Proteínas Cromossômicas não Histona/genética , Segregação de Cromossomos/genética , DNA Arqueal/química , DNA Super-Helicoidal/química , DNA Super-Helicoidal/genética , Kluyveromyces/genética , Conformação de Ácido Nucleico , Estrutura Terciária de ProteínaRESUMO
Eukarya and, more recently, some bacteria have been shown to rely on a cytoskeleton-based apparatus to drive chromosome segregation. In contrast, the factors and mechanisms underpinning this fundamental process are underexplored in archaea, the third domain of life. Here we establish that the archaeon Sulfolobus solfataricus harbors a hybrid segrosome consisting of two interacting proteins, SegA and SegB, that play a key role in genome segregation in this organism. SegA is an ortholog of bacterial, Walker-type ParA proteins, whereas SegB is an archaea-specific factor lacking sequence identity to either eukaryotic or bacterial proteins, but sharing homology with a cluster of uncharacterized factors conserved in both crenarchaea and euryarchaea, the two major archaeal sub-phyla. We show that SegA is an ATPase that polymerizes in vitro and that SegB is a site-specific DNA-binding protein contacting palindromic sequences located upstream of the segAB cassette. SegB interacts with SegA in the presence of nucleotides and dramatically affects its polymerization dynamics. Our data demonstrate that SegB strongly stimulates SegA polymerization, possibly by promoting SegA nucleation and accelerating polymer growth. Increased expression levels of segAB resulted in severe growth and chromosome segregation defects, including formation of anucleate cells, compact nucleoids confined to one half of the cell compartment and fragmented nucleoids. The overall picture emerging from our findings indicates that the SegAB complex fulfills a crucial function in chromosome segregation and is the prototype of a DNA partition machine widespread across archaea.
