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Cytokinesis in many eukaryotes requires a contractile actomyosin ring that is placed at the division site. In fission yeast, which is an attractive organism for the study of cytokinesis, actomyosin ring assembly and contraction requires the myosin II heavy chain Myo2p. Although myo2-E1, a temperature-sensitive mutant defective in the upper 50 kDa domain of Myo2p, has been studied extensively, the molecular basis of the cytokinesis defect is not understood. Here, we isolate myo2-E1-Sup2, an intragenic suppressor that contains the original mutation in myo2-E1 (G345R) and a second mutation in the upper 50 kDa domain (Y297C). Unlike myo2-E1-Sup1, a previously characterized myo2-E1 suppressor, myo2-E1-Sup2 reverses actomyosin ring contraction defects in vitro and in vivo. Structural analysis of available myosin motor domain conformations suggests that a steric clash in myo2-E1, which is caused by the replacement of a glycine with a bulky arginine, is relieved in myo2-E1-Sup2 by mutation of a tyrosine to a smaller cysteine. Our work provides insight into the function of the upper 50 kDa domain of Myo2p, informs a molecular basis for the cytokinesis defect in myo2-E1, and may be relevant to the understanding of certain cardiomyopathies., Summary: An unbiased genetic screen uncovers a mutation that reverses a steric clash in the myosin II motor head, which was previously reported to cause defective actomyosin ring-dependent cytokinesis in fission yeast.

Waterborne illness is one of the world's most pervasive causes of morbidity and mortality, with severe health, social, environmental and economic impacts. Human faeces are often inadequately managed and contaminate community and household water supplies. Sustainable safe community and household water access is often not achieved in the developing world and adverse health impacts can result from faecal contamination of water. Metals, particularly copper and zinc, have been proposed as effective disinfectants of drinking water. This research aimed to quantify the overall disinfecting effects of a 0.2 mg/L and 2mg/L dose of copper and zinc oxide nanoparticles, as well as the kinetics of such disinfection, on three test organisms; Bacillus cereus spores, Escherichia coli log-phase cells, and MS2 coliphage. Experiments were conducted in pH 7.3, 10 g/L (approximately 42mM)HEPES-buffered water with and without about 10 mg/L added natural organic matter (NOM). The concentrations of culturable microorganisms were assayed at 0, 20, 60, 180, and 360 minutes. Copper and zinc oxide nanoparticles were found to be effective for same-day or overnight achievement of the World Health Organisation (W.H.O.) "protective" level of disinfection (2 log[10] or 99% reduction) for E. coli in both experimental waters, and B. cereus spores in waters without added NOM. Measurable inactivation was not observed against MS2 coliphage for the low dose, although some inactivation (0.53 to 0.78 log[10] reduction in 6 hours in NOM-amended and NOM-negative waters, respectively) was achieved at the high dose. Some other experimental conditions yielded inactivation, but it was not rapid or extensive enough to achieve the W.H.O. protective performance target for same-day or overnight use. Overall, the combined use of copper and zinc nanoparticles shows promise for effective point-of-use disinfection of water low in turbidity and natural organic matter.

We examined whether C-terminal residues of soluble recombinant FtsZ of Mycobacterium tuberculosis (MtFtsZ) have any role in MtFtsZ polymerization in vitro. MtFtsZ-delta C1, which lacks C-terminal extreme Arg residue (underlined in the C-terminal extreme stretch of 13 residues, DDDDVDVPPFMRR), but retaining the penultimate Arg residue (DDDDVDVPPFMR), polymerizes like full-length MtFtsZ in vitro. However, MtFtsZ-delta C2 that lacks both the Arg residues at the C-terminus (DDDDVDVPPFM), neither polymerizes at pH 6.5 nor forms even single- or double-stranded filaments at pH 7.7 in the presence of 10 mM CaCl2. Neither replacement of the penultimate Arg residue, in the C-terminal Arg deletion mutant DDDDVDVPPFMR, with Lys or His or Ala or Asp (DDDDVDVPPFMK/H/A/D) enabled polymerization. Although MtFtsZ-delta C2 showed secondary and tertiary structural changes, which might have affected polymerization, GTPase activity of MtFtsZ-delta C2 was comparable to that of MtFtsZ. These data suggest that MtFtsZ requires an Arg residue as the extreme C-terminal residue for polymerization in vitro. The polypeptide segment containing C-terminal 67 residues, whose coordinates were absent from MtFtsZ crystal structure, was modeled on tubulin and MtFtsZ dimers. Possibilities for the influence of the C-terminal Arg residues on the stability of the dimer and thereby on MtFtsZ polymerization have been discussed.