title: Discovery of two novel families of proteins that are proposed to interact with prokaryotic SMC proteins, and characterization of the Bacillus subtilis family members ScpA and ScpB.
abstract: Structural maintenance of chromosomes (SMC) proteins are present in all eukaryotes and in many prokaryotes. Eukaryotic SMC proteins form complexes with various non-SMC subunits, which affect their function, whereas the prokaryotic homologues had no known non-SMC partners and were thought to act as simple homodimers. Here we describe two novel families of proteins, widespread in archaea and (Gram-positive) bacteria, which we denote 'segregation and condensation proteins' (Scps). ScpA genes are localized next to smc genes in nearly all SMC- containing archaea, suggesting that they belong to the same operon and are thus involved in a common process in the cell. The function of ScpA was studied in Bacillus subtilis, which also harbours a well characterized smc gene. Here we show that scpA mutants display characteristic phenotypes nearly identical to those of smc mutants, including temperature- sensitive growth, production of anucleate cells, formation of aberrant nucleoids, and chromosome splitting by the so-called guillotine effect. Thus, both SMC and ScpA are required for chromosome segregation and condensation. Interestingly, mutants of another B. subtilis gene, scpB, which is localized downstream from scpA, display the same phenotypes, which indicate that ScpB is also involved in these functions. ScpB is generally present in species that also encode ScpA. The physical interaction of ScpA and SMC was proven (i) by the use of the yeast two-hybrid system and (ii) by the isolation of a complex containing both proteins from cell extracts of B. subtilis. By extension, we speculate that interaction of orthologues of the two proteins is important for chromosome segregation in many archaea and bacteria, and propose that SMC proteins generally have non-SMC protein partners that affect their function not only in eukaryotes but also in prokaryotes.
authors.affiliation: J. W. Goethe-Universität, Biozentrum, Institut für Mikrobiologie, Franfurt, Germany. soppa@em.uni-frankfurt.de
authors.forename: Jörg
authors.initials: J
authors.lastname: Soppa
authors.forename: Kazuo
authors.initials: K
authors.lastname: Kobayashi
authors.forename: Marie-Françoise
authors.initials: MF
authors.lastname: Noirot-Gros
authors.forename: Dieter
authors.initials: D
authors.lastname: Oesterhelt
authors.forename: S Dusko
authors.initials: SD
authors.lastname: Ehrlich
authors.forename: Etienne
authors.initials: E
authors.lastname: Dervyn
authors.forename: Naotake
authors.initials: N
authors.lastname: Ogasawara
authors.forename: Shigeki
authors.initials: S
authors.lastname: Moriya
mesh_terms: D000595:Amino Acid Sequence; D019843:Archaeal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001412:Bacillus subtilis / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D020090:Chromosome Segregation; D002876:Chromosomes, Bacterial; D008969:Molecular Sequence Data; D009154:Mutation; D010802:Phylogeny; D011387:Prokaryotic Cells / Q000378:metabolism*; D017422:Sequence Analysis, DNA; D020798:Two-Hybrid System Techniques
chemical_list: D019843:Archaeal Proteins; D001426:Bacterial Proteins; D018797:Cell Cycle Proteins; C118650:SMC protein, Bacteria