Search

The histone variant macroH2A has been found to play important regulatory roles in genomic processes, especially in regulating transcriptomes. However, whether macroH2A nucleosomes are retained on mitotic chromosomes to enable maintenance of cell-specific transcriptomes is not known. Here, examining mouse embryonic fibroblast cells (NIH-3T3) with native chromatin immunoprecipitation and sequencing (nChIP-seq), we show that the overwhelming majority (~90%) of macroH2A1 domains identified at the G1/S stage are indeed stably retained on mitotic chromosomes. Unexpectedly though, we also find that there are a number of macroH2A domains that are specific for either mitotic or G1/S cells. Notably, more than 7,000 interphase expressed genes flanked by macroH2A1 domains are loaded with macroH2A1 nucleosomes on the mitotic chromosome to form extended domains. Overall, these results reveal that, while the majority of macroH2A1 domains are indeed faithfully transmitted through the mitotic chromosomes, there is a previously unknown cell-cycle dependent exchange of macroH2A1 nucleosomes at numerous genomic loci, indicating the existence of molecular machineries for this dynamically regulated process. We anticipate that these findings will prove to be essential for the integrity of mitotic progression and the maintenance of cellular identity. [ABSTRACT FROM AUTHOR]

The purpose of this study was to determine whether steric blockage of one head by the second head of native two-headed myosin was responsible for the inactivity of nonphosphorylated two-headed myosin compared with the high activity of single-headed myosin, as suggested on the basis of electron microscopy of two-dimensional crystals of heavy meromyosin (Wendt, T., Taylor, D., Messier, T., Trybus, K. M., and Taylor, K. A. (1999) J. Cell Biol. 147, 1385-1390; and Wendt, T., Taylor, D., Trybus, K. M., and Taylor, K. (2001) Proc. Natl. Acad. Sci. U. S. A. 98, 4361-4366). Our earlier cryo-atomic force microscopy (cryo-AFM) (Zhang, Y., Shao, Z., Somlyo, A. P., and Somlyo, A. V. (1997) Biophys. J. 72, 1308-1318) indicates that thiophosphorylation of the regulatory light chain increases the separation of the two heads of a single myosin molecule, but the thermodynamic probability of steric hindrance by strong binding between the two heads was not determined. We now report this probability determined by cryo-AFM of single whole myosin molecules shown to have normal low ATPase activity (0.007 s[sup -1]). We found that the thermodynamic probability of the relative head positions of nonphosphorylated myosin was approximately equal between separated heads as compared with closely apposed heads (energy difference of 0.24 kT (where k is a Boltzman constant and T is the absolute temperature)), and thiophosphorylation increased the number of molecules having separated heads (energy advantage of -1.2 kT (where k is a Boltzman constant and I is the absolute temperature)). Our results do not support the suggestion that strong binding of one head to the other stabilizes the blocked conformation against thermal fluctuations resulting in steric blockage that can account for the low activity of nonphosphorylated two-headed myosin. [ABSTRACT FROM AUTHOR]

Discusses the role of GXXG motif for membrane channel formation by Helicobacter pylori vacuolating (VacA) toxin. Identification of VacA amino acids required for transmembrane protein dimerization in a TOXCAT model system; Role of the VacA amino-terminal hydrophobic region in vacuolating cytotoxic activity; Role of the VacA amino-terminal hydrophobic region in formation of channels in planar lipid bilayers.

Demonstrates that stable, soluble septin heterodimers can be produced by co-expression from bicistronic vectors in bacteria and that the co-expression of three septins results in their assembly into filaments. Binding of guanine nucleotide and show guanosine triphosphatase activity by pre-assembled dimers and trimers; Analysis of pertinent topics and relevant issues; Implications on the molecular basis of cell and developmental biology.

Examines the difference in the capacity of type s1 and type s2 Helicobacter pylori VacA proteins to form anion-selective membrane channels. Electrophysiologic properties of channels formed by wild-type and chimeric VacA toxins; Dominant-negative phenotype of the type s2/m1 VacA toxin; Protein-protein interactions between different toxin species.