8 research outputs found
Constraints, Histones, and the 30 Nanometer Spiral
We investigate the mechanical stability of a segment of DNA wrapped around a
histone in the nucleosome configuration. The assumption underlying this
investigation is that the proper model for this packaging arrangement is that
of an elastic rod that is free to twist and that writhes subject to mechanical
constraints. We find that the number of constraints required to stabilize the
nuclesome configuration is determined by the length of the segment, the number
of times the DNA wraps around the histone spool, and the specific constraints
utilized. While it can be shown that four constraints suffice, in principle, to
insure stability of the nucleosome, a proper choice must be made to guarantee
the effectiveness of this minimal number. The optimal choice of constraints
appears to bear a relation to the existence of a spiral ridge on the surface of
the histone octamer. The particular configuration that we investigate is
related to the 30 nanometer spiral, a higher-order organization of DNA in
chromatin.Comment: ReVTeX, 15 pages, 18 figure
Nucleosomes in gene regulation: theoretical approaches
This work reviews current theoretical approaches of biophysics and
bioinformatics for the description of nucleosome arrangements in chromatin and
transcription factor binding to nucleosomal organized DNA. The role of
nucleosomes in gene regulation is discussed from molecular-mechanistic and
biological point of view. In addition to classical problems of this field,
actual questions of epigenetic regulation are discussed. The authors selected
for discussion what seem to be the most interesting concepts and hypotheses.
Mathematical approaches are described in a simplified language to attract
attention to the most important directions of this field
Intracellular innate resistance to bacterial pathogens
Mammalian innate immunity stimulates antigen-specific immune responses and acts to control infection prior to the onset of adaptive immunity. Some bacterial pathogens replicate within the host cell and are therefore sheltered from some protective aspects of innate immunity such as complement. Here we focus on mechanisms of innate intracellular resistance encountered by bacterial pathogens and how some bacteria can evade destruction by the innate immune system. Major strategies of intracellular antibacterial defence include pathogen compartmentalization and iron limitation. Compartmentalization of pathogens within the host endocytic pathway is critical for generating high local concentrations of antimicrobial molecules, such as reactive oxygen species, and regulating concentrations of divalent cations that are essential for microbial growth. Cytosolic sensing, autophagy, sequestration of essential nutrients and membrane attack by antimicrobial peptides are also discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71916/1/j.1462-5822.2006.00795.x.pd
Deletion of the unique gene encoding a typical histone H1 has no apparent phenotype in Aspergillus nidulans
We have cloned the H1 histone gene (hhoA) of Aspergillus nidulans. This single-copy gene codes for a typical linker histone with one central globular domain. The open reading frame is interrupted by six introns. The position of the first intron is identical to that of introns found in some plant histones. An H1–GFP fusion shows exclusive nuclear localization, whereas chromosomal localization can be observed during condensation at mitosis. Surprisingly, the deletion of hhoA results in no obvious phenotype. The nucleosomal repeat length and susceptibility to micrococcal nuclease digestion of A. nidulans chromatin are unchanged in the deleted strain. The nucleosomal organization of a number of promoters, including in particular the strictly regulated niiA-niaD bidirectional promoter is not affected.This work was supported by EC grant BIO2-CT93-0147, the CNRS and the Université Paris Sud. M.I.M-P. has been the recipient of CE fellowship BIO-CT-94-8102 and a fellowship from the Fondation pour la Recherche Médicale. R.G. has been the recipient of CE fellowship BIO4-CT-96-5010Peer reviewe