Myxococcus xanthus is a gram-negative bacterium which, upon starvation, undergoes a spectacular developmental cycle culminating in the formation of spore-filed fruiting bodies. We recently characterized a protein serine-threonine kinase (Pknl) that is required for normal development (J. Munoz-Dorado, S. Inouye, and M. Inouye, Cell 67: [995][996][997][998][999][1000][1001][1002][1003][1004][1005][1006] 1991). pknl was cloned by polymerase chain reaction amplification with primers designed from conserved sequences in eukaryotic protein kinases. In this study, a fragment of thepknl gene and an oligonucleotide corresponding to another highly conserved region were employed as probes for Southern blot analyses, which indicated that there are at least 26 putative kinase genes in M. xanthus. Most of the putative kinase genes were cloned, and complete or partial sequencing of eight clones revealed that they indeed contained highly conserved sequences present in eukaryotic kinases. These results suggest that complex kinase cascades similar to those described for eukaryotes might be involved in regulation of the M. xanthus life cycle.

In this paper we continue the analysis of the two-scale method for the Monge-Ampère equation for dimension d ≥ 2 introduced in [12]. We prove continuous dependence of discrete solutions on data that in turn hinges on a discrete version of the Alexandroff estimate. They are both instrumental to prove pointwise error estimates for classical solutions with Hölder and Sobolev regularity. We also derive convergence rates for viscosity solutions with bounded Hessians which may be piecewise smooth or degenerate.

Ion channel hyperactivation can result in neuronal loss in injury, stroke and neurodegenerative disease. Acidosis-associated hyperactivation of the Degenerin/epithelial amiloride-sensitive Na þ channel (DEG/ENaC) acid-sensing ion channel 1a (ASIC1a), a proton-gated channel expressed in the mammalian brain, contributes significantly to neuronal loss in ischemia. Analogously, in invertebrates, genetic hyperactivation of the Caenorhabditis elegans mechanosensory (MEC) channel (MEC-4(d)) of the DEG/ ENaC ion channel superfamily induces neuronal necrosis. Similarly substituted MEC-10(d) mutant subunits of the same MEC channel are only marginally neurotoxic, and we therefore exploited the weak necrosis phenotype of mec-10(d) lines to screen for novel extragenic mutations that enhance neuronal death. Here, we report on one mec-10(d) necrosis enhancer, which we show is MEC-4 variant MEC-4(A149V). MEC-4(A149V) executes normal MEC-4 function in touch sensation and does not induce necrosis on its own, but rather combines with MEC-10(d) to create a strongly neurotoxic channel. The MEC-4(A149V) þ MEC-10(d) channel conducts elevated Na þ and Ca 2 þ currents (with a disproportionate increase in Ca 2 þ current) in the Xenopus oocyte expression system, and exhibits altered binding of the channel inhibitor amiloride. Our data document the first example of synergistically toxic intersubunit interactions in the DEG/ENaC channel class and provide evidence that Ca 2 þ current levels may be decisive factors in tipping the balance between neuronal survival and necrosis. Ion channel dysfunction can result in the neuronal death that underlies the devastating consequences of stroke and nervous system injury. Primary determinants of mammalian neuronal loss associated with ion channel hyperactivation include the glutamate-gated channels 1 and the less extensively studied ASIC (acid-sensing ion channels) 2 of the DEG/ ENaC superfamily (named after founding members Caenorhabditis elegans degenerins and the mammalian epithelial amiloride-sensitive Na þ channels). DEG/ENaC channel complexes include three DEG/ENaC subunits, 3 with each subunit having a large extracellular domain, two transmembrane domains that contribute to the channel pore, and intracellular N and C termini (reviewed in Kellenberger and Schild 4 ). Structure/activity studies in the DEG/ENaC channel class have provided insights into function, but the relationship between toxicity and subunit interactions is largely unexplored.Of DEG/ENaCs studied to date, the C. elegans MEC channel, which transduces gentle touch stimuli in six mechanosensory (MEC) neurons 5,6 has been analyzed in most genetic detail. The core of the MEC channel is formed by DEG/ENaC subunits MEC-4 7,8 and MEC-10, 9 which associate with paraoxonase-like transmembrane protein MEC-6 10 and stomatin-like protein MEC-2.7,11,12 Dominant gain-offunction mutations alter MEC-4(A713) (the d position) to introduce large amino acids (AAs) near the channel pore, causing channel hyperactivity that induces necrotic-like neurod...