title: Mycobacterium smegmatis histone-like protein Hlp is nucleoid associated.
abstract: Eubacteria encode proteins that are required for nucleoid organization and for regulation of DNA-dependent processes. Of these histone-like proteins (Hlps), Escherichia coli HU has been shown to associate with the nucleoid and to regulate processes such as DNA repair and recombination. In contrast, the divergent HU homologs encoded by mycobacteria have been variously identified as involved in the physiology of dormancy, in the response to cold shock, or as laminin-binding proteins associated with the cell envelope. We show here, contrary to previous reports that the HU-related Hlp from Mycobacterium smegmatis associates with the nucleoid in vivo. Using indirect fluorescent antibody microscopy we show that cold shock causes Hlp to accumulate in the cytoplasm of M. smegmatis. No evidence of surface-associated Hlp was found in M. smegmatis cells treated for cell wall permeabilization. Quantitative Western blots indicate that exponentially growing cells contain c. 120 molecules per cell, with upregulation of Hlp after cold shock estimated to be c. 10-fold. That Hlp associates with the nucleoid in vivo suggests functions in DNA metabolism, perhaps in adaptation to environmental stress.
authors.affiliation: Department of Biological Sciences, Louisiana State University, Baton Rouge, LA 70803, USA.
authors.forename: Anirban
authors.initials: A
authors.lastname: Mukherjee
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: DiMario
authors.forename: Anne
authors.initials: A
authors.lastname: Grove
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002466:Cell Nucleolus / Q000235:genetics / Q000378:metabolism*; D006657:Histones / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D020102:Mycobacterium smegmatis / Q000737:chemistry / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D021381:Protein Transport; D017386:Sequence Homology, Amino Acid
chemical_list: D001426:Bacterial Proteins; D006657:Histones