We present a technique by which it is possible to produce a planar sensor for ion channel electrophysiology from glass substrates. Apertures with diameters in the low micrometer to submicrometer range are achieved by irradiation of a glass chip with a single heavy ion and subsequent wet track etching. The function of the device is demonstrated by recordings of single channel currents mediated by the model ion channel gramicidin A in lipid bilayers spanning the micromachined aperture.

Effects of neutralization on butadiene–methacrylic acid copolymers have been studied. In Hycar CTB with 2% acid groups, small‐angle x‐ray scattering gives evidence of some cation clustering and leads to a value of the mean radius of 5.6 Å for the clusters and a value of the distance between them of 70 Å. When the concentration of salt is increased there is no appreciable change in the distance between clusters or in their size, but their number increases. The structure of clusters has been studied by electron paramagnetic resonance in copolymers neutralized with copper salts. The appearance of a line as in the monohydrated acetate salt permits one to define the structure of clusters consisting of two Cu2+ and four RCOO− ions with two H2O or RCOOH molecules. When the temperature is increased, the signal corresponding to Cu2+–Cu2+ pairs disappears. In high molecular weight butadiene methacrylic acid copolymers with 9% acid groups, we have found the ion pair clusters gathered into larger clusters. In dynamic mechanical properties, a relaxation peak appears at 340°K. We interpret this as due to breaking and possible re‐forming of dipolar associations.

Proteins can be crosslinked by chemical compounds without any accompanying change in the complicated three-dimensional structure. Many bifunctional reagents that can react with functional groups in the side chains of the amino acids are now known. Not only can the distance between the linked amino acid residues be deduced from the known length ofthe bridge introduced, but information can also be obtained concerning changes in conformation during other reactions and concerning the arrangement of the components of a quaternary structure.Angew. Chem. internat. Edit. / Yo!. I0 (1971) / N o . 11 795

The nuclear envelope (NE) separates the two major compartments of eukaryotic cells, the nucleus and the cytoplasm. Recent studies suggest that the uptake of nuclear proteins into the nucleus is initiated by binding of nuclear location signals (NLSs) contained within these proteins to receptors in the NE, followed by translocation through the nuclear pore complex. To examine the binding step without interference from intranuclear events, we have used a system consisting of (i) purified rat liver NEs fixed onto glass slides and (it) the prototype simian virus 40 large T antigen (SV40 T) NLS conjugated to nonnuclear carrier proteins, and we have visualized the receptor-ligand interaction by indirect immunofluorescence. In this system, incubation of isolated NEs with the wild-type SV40 T NLS conjugate with carrier proteins resulted in binding that was signal sequence-dependent, could be competitively blocked with excess conjugated and unconjugated wild-type peptide, did not require ATP, and was not affected by the transport-inhibiting lectin wheat germ agglutinin. In contrast, only minimal binding was observed with a mutant SV40 T NLS conjugate. These results are consistent with those obtained in other, more complex in vitro systems and suggest that binding of the SV40 T NLS is receptor-mediated. Binding is largely abolished by extraction of the NE with the nonionic detergent Triton X-100, suggesting that the receptor is soluble in detergent. We find in the Triton X-100 supernatant four major NLS-binding proteins with apparent molecular masses of 76, 67, 59, and 58 kDa by photoaffinity labeling with a highly specific crosslinker, azido-NLS. The reduced complexity of the system described here should be useful for the functional study of other potential NLSs for the identification and isolation of their binding sites and for the screening of antibodies raised against these binding sites.The selective exchange of molecules across the nuclear envelope (NE) is an essential factor in many cellular processes. Recent studies have shown that the regulation of these processes is mediated, at least in part, by the interaction of signal sequences contained within these molecules with receptors localized in the NE.The four ultrastructurally distinct components of the NE are the outer and the inner nuclear membrane, the nuclear lamina, and the nuclear pore complexes (reviewed in ref. 1). It is generally agreed that the pore complexes provide aqueous channels through which nucleocytoplasmic exchanges, including macromolecular exchanges, take place (1-4), and there is electron microscopic evidence to support this (5-10).Studies on the movement of molecules from cytoplasm to nucleus have established that pore complexes have channels of about 9-12 nm in diameter available for passive diffusion (11,12). Globular proteins with molecular masses < 15 kDa will diffuse at roughly the same rate as in free solution, but proteins larger than -60 kDa are too big to diffuse through the pore complexes (11). However, certain high molecula...