A putative GDP-GTP exchange factor is required for development of the excretory cell in Caenorhabditis elegans.

The Caenorhabditis elegans excretory cell extends tubular processes, called canals, along the basolateral surface of the epidermis. Mutations in the exc-5 gene cause tubulocystic defects in this canal. Ultrastructural analysis suggests that exc-5 is required for the proper placement of cytoskeletal elements at the apical epithelial surface. exc-5 encodes a protein homologous to guanine nucleotide exchange factors and contains motif architecture similar to that of FGD1, which is responsible for faciogenital dysplasia. exc-5 interacts genetically with mig-2, which encodes Rho GTPase. These results suggest that EXC-5 controls the structural organization of the excretory canal by regulating Rho family GTPase activities.

Cystic canal mutants in Caenorhabditis elegans are defective in the apical membrane domain of the renal (excretory) cell.

The excretory cell extends a tubular process, or canal, along the basolateral surface of the epidermis to form the nematode renal epithelium. This cell can undergo normal tubulogenesis in isolated cell culture. Mutations in 12 genes cause excretory canal cysts in Caenorhabditis elegans. Genetic interactions, and their similar phenotypes, suggest these genes may encode functionally related proteins. Depending upon genotype and individual canal, defects range from focal cysts, flanked by normal width segments, to regional cysts involving the entire tubule. Oftentimes the enlarged regions are convoluted or partially septated. In mutants with very large cysts, renal function is measurably impaired. Based on histology and ultrastructure, canal cysts likely result from defects of the apical membrane domain. These mutants provide a model of tubulocystic disease without hyperplasia or basement membrane abnormalities. Similar apical mechanisms could regulate tubular morphology of vertebrate nephrons.

Effect of outer membrane permeability on chemotaxis in Escherichia coli.

The relationship between outer membrane permeability and chemotaxis in Escherichia coli was studied on mutants in the major porin genes ompF and ompC. Both porins allowed passage of amino acids across the outer membrane sufficiently to be sensed by the methyl-accepting chemotaxis proteins, although OmpF was more effective than OmpC. A mutant deleted for both ompF and ompC, AW740, was almost completely nonchemotactic to amino acids in spatial assays. AW740 required greater stimulation with L-aspartate than did the wild type to achieve full methylation of methyl-accepting chemotaxis protein II. Induction of LamB protein allowed taxis to maltose but not to L-aspartate, which indicates that the maltoporin cannot rapidly pass aspartate. Salt taxis was less severely inhibited by the loss of porins than was amino acid taxis, which implies an additional mechanism of outer membrane permeability. These results show that chemotaxis can be used as a sensitive in vivo assay for outer membrane permeability to a range of compounds and imply that E. coli can regulate chemotactic sensitivity by altering the porin composition of the outer membrane.

Ion channel activities in the Escherichia coli outer membrane.

The electrical properties of Escherichia coli cells were examined by the patch-clamp technique. Giant cells or giant spheroplasts were generated by five different methods. By electron micrographic and other criteria we determined that the patches are most likely from the outer membrane. We regularly observed currents through at least two types of channels in this membrane. The first current is mechanosensitive and voltage-dependent, and can be observed in single gene mutants of the known major porins (ompF, ompC, phoE, lamB); this channel may represent a minor porin or a new class of outer membrane protein. The possible identity of the second, voltage-sensitive channel with one of the known outer membrane proteins is being explored. The high-resistance seals consistently formed on these patches and the presence of gated ion channels suggest that most of the pores of the outer membrane are not statically open, as commonly held, but are closed at rest and may be openable by physiological stimuli.

Pressure-sensitive ion channel in Escherichia coli.

We have used the patch-clamp electrical recording technique on giant spheroplasts of Escherichia coli and have discovered pressure-activated ion channels. The channels have the following properties: activation by slight positive or negative pressure; voltage dependence; large conductance; selectivity for anions over cations; dependence of activity on the species of permeant ions. We believe that these channels may be involved in bacterial osmoregulation and osmotaxis.

The territorial defense hypothesis and the ecology of insular vertebrates.

Insular lizards, birds, and mammals in high-density populations often exhibit reduced situation-specific aggression toward conspecifics. This aggressive behavior can be expressed in the form of (1) reduced territory sizes, (2) increased territory overlap with neighbors, (3) acceptance of subordinates on the territory, (4) reduced aggressiveness to certain classes of conspecifics, or (5) abandonment of territorial defense. These behavioral traits can be explained by two nonexclusive hypotheses. The resource hypothesis suggests that territorial behavior is primarily adjusted to resource densities, and that resources are more abundant on islands than on the mainland (e.g., because of a lack of competing species). The defense hypothesis suggests that, in addition to any effects of resources, the costs of defense against both territorial intruders and contenders for vacant territories are higher on islands. Recent theoretical and empirical studies indicate that these behavioral changes can occur as a result of elevated defense costs, independent of resource densities. Reduced predation, more benign climates, and an absence of habitat sinks on islands would all tend to increase the density of potential intruders and contenders, and hence the costs of defense for owners of insular territories. The two hypotheses differ in their predictions about the rates of biomass production (growth or reproduction) for holders of insular territories. Reproductive and growth data from insular-mainland pairs indicate the importance of elevated defense costs, and also suggest that many insular vertebrates reallocate their breeding resources so as to produce young that are more competitive. The suite of ecological and behavioral traits exhibited by insular territorial vertebrates can best be explained by three factors operating in concert: higher available resource densities, higher defense costs, and (sometimes) a reallocation of resources to produce young that are more competitive.

Copper(II).bleomycin, iron(III).bleomycin, and copper(II).phleomycin: comparative study of deoxyribonucleic acid binding.

The kinetics and mechanism of binding of Cu-(II).bleomycin, Fe(III).bleomycin, and Cu(II).phleomycin to DNA were studied by using fluorometry, equilibrium dialysis, electric dichroism, and temperature-jump and stopped-flow spectrophotometry. The affinity of Cu(II).bleomycin for DNA was greater than that of metal-free bleomycin but less than that of Fe(III).bleomycin. Cu(II).bleomycin exhibited a two-step binding process, with the slow step indicating a lifetime of 0.1 s for the Cu(II).bleomycin.DNA complex. Fe(III).bleomycin binding kinetics indicated the presence of complexes having lifetimes of up to 22 s. DNA was lengthened by 4.6 A/molecule of bound Cu(II).bleomycin and by 3.2 A/bound Fe(III).bleomycin but not at all by Cu(II).phleomycin, suggesting that both bleomycin complexes intercalate while the phleomycin complex does not. However, phleomycin exhibited nearly the same specificity of DNA base release as bleomycin. These results suggest that the coordinated metal ion plays a major role in the binding of metal-bleomycin complexes to DNA but that intercalation is neither essential for DNA binding and degradation nor primarily responsible for the specificity of DNA base release by these drugs.