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

Authors

  • Jörg Soppa,

    1. J. W. Goethe-Universität, Biozentrum, Institut für Mikrobiologie, D-60439 Frankfurt, Germany.
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    • For correspondence. *For characterization of the protein families. E-mail soppa@em.uni-frankfurt.de; Tel./Fax (+49) 69 798 29564.

    • Both authors contributed equally to this work.

  • Kazuo Kobayashi,

    1. Graduate School of Biological Sciences, Nara Institute of Science and Technology, Ikoma, Nara 630–0101, Japan.
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    • Both authors contributed equally to this work.

  • Marie-Françoise Noirot-Gros,

    1. Laboratoire de Génétique Microbienne, INRA, Domaine de Vilvert, 78352 Jouy-en-Josas cedex, France.
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  • Dieter Oesterhelt,

    1. Max-Planck-Institut für Biochemie, D-82152 Martinsried, Germany.
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  • S. Dusko Ehrlich,

    1. Laboratoire de Génétique Microbienne, INRA, Domaine de Vilvert, 78352 Jouy-en-Josas cedex, France.
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  • Etienne Dervyn,

    1. Laboratoire de Génétique Microbienne, INRA, Domaine de Vilvert, 78352 Jouy-en-Josas cedex, France.
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  • Naotake Ogasawara,

    1. Graduate School of Biological Sciences, Nara Institute of Science and Technology, Ikoma, Nara 630–0101, Japan.
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  • Shigeki Moriya

    1. Graduate School of Biological Sciences, Nara Institute of Science and Technology, Ikoma, Nara 630–0101, Japan.
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    • **For characterization of B. subtilis mutants. E-mail moriya@bs.aist-nara.ac.jp; Tel. (+81) 743 72 5432; Fax (+81) 743 72 5439.


Summary

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.

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