Spatial distribution and size of acetylcholine receptor clusters determined by motor nerves in developing chick muscles

The size and distribution of acetylcholine receptor clusters (AChR-C) on normal and aneural developing muscle fibres of the chick wing were studied by labelling AChR with fluorescent conjugates of alpha-bungarotoxin (alpha-BGT). AChR-C of a size typical of initial synaptic contacts (5 micron long) were present at 7 days incubation, shortly after the appearance of nerves, and were grouped in bands corresponding to muscle nerve branches. A regular distribution of large (approximately equal to 5 micron) AChR-C separated by 100-200 micron had developed by 10-14 days in the slow-tonic anterior latissimus dorsi and ulnimetacarpalis dorsalis muscles. The role of motor innervation in the formation of AChR-C was assessed by removing the brachial neural tube at 2 days incubation in order to prevent nerves entering the wing. Neural-tube removal prevented the appearance of the large AChR-C normally associated with the early synaptic contacts. Small AChR-C (less than 2 micron long) appeared in aneural muscles, but these were not grouped into bands characteristic of the large AChR-C in normal muscles. The results suggest that the formation of junctional AChR-C is dependent on nerves.

31P and two-dimensional 31P/1H correlated NMR spectra of Duplex d(Ap[17O]Gp[18O]Cp[16O]T) and assignment of 31P signals in d(ApGpCpT)2-actinomycin D complex

A solid-phase phosphoramidite method was used for the synthesis of unlabeled and phosphoryl-labeled d(Ap-[17O]Gp[18O]Cp[16O]T). The ability to label the phosphoryl oxygens of d(ApGpCpT) and thus assign the 31P signals, combined with a two-dimensional 31P/1H chemical shift correlated NMR spectral technique, provided a novel means for the ready assignment of the H5' and H3' protons coupled to the phosphates. Phosphoryl labeling has also allowed us to assign the 31P NMR signals in the actinomycin D-d(Ap-[17O]Gp[18O]Cp[16O]T)2 duplex complex and confirm that the drug intercalates between the GpC stacked base pairs.

A two-dimensional NMR method for assignment of deoxyribose proton NMR signals in d(ApGpCpT)

The ability to label the phosphoryl oxygens of d( ApGpCpT ) and thus assign the 31P signals, combined with a 2-D 31P/1H chemical shift correlated NMR spectral technique, provides a novel means for the ready assignment of the H5' and H3' protons coupled to the phosphates.

Phosphorus-31 nuclear magnetic resonance of double- and triple-helical nucleic acids. Phosphorus-31 chemical shifts as a probe of phosphorus-oxygen ester bond torsional angles

The temperature dependence to the 31P NMR spectra of poly[d(GC)] . poly [d(GC)],d(GC)4, phenylalanine tRNA (yeast) and mixtures of poly(A) + oligo(U) is presented. The 31P NMR spectra of mixtures of complementary RNA and of the poly d(GC) self-complementary DNA provide torsional information on the phosphate ester conformation in the double, triple, and "Z" helix. The increasing downfield shift with temperature of the single-strand nucleic acids provides a measure of the change in the phosphate ester conformation in the single helix to coil conversion. A separate upfield peak (20-60% of the total phosphates) is observed at lower temperatures in the oligo(U) . poly(A) mixtures which is assigned to the double helix/triple helix. Proton NMR and UV spectra confirm the presence of the multistrand forms. The 31P chemical shift for the double helix/triple helix is 0.2-0.5 ppm upfield from the chemical shift for the single helix which in turn is 1.0 ppm upfield from the chemical shift for the random coil conformation.