An approach for time-resolved x-ray scattering.

Recent biological optical spectroscopic studies have correlated discrete spectroscopic states with biological function in several systems. One of the challenges of molecular biophysics is to correlate structural changes with these spectroscopic states. From small-angle x-ray scattering one can obtain a key structural parameter, the radius of gyration of solubilized proteins. The method described in this paper would permit determination small changes in the radius using polychromatic synchrotron radiation. The high flux of the storage ring combined with an enhancement factor of approximately 10(4), obtained by removing the requirement for monochromatic radiation, will permit determining the radius on a millisecond time scale. Unlike energy-dispersive methods, this method would use all available energies over a wide range of angles.     

An x-ray crystallographic study of hemerythrin.

The non-heme iron protein, hemerythrin, has been crystallized from Themiste dyscritum. The crystals belong to the tetragonal space group P4 with unit cell dimensions $\text{a = b = 86.5}\text{A}\text{̊}\text{, c = 80.6}\text{A}\text{̊}$. A 2-fold molecular axis is suggested, implying that the asymmetric unit contains four subunits each with a molecular weight of 12,600.     

Improvement of the contrast of electron microscope images by the optical shadow method

Amplitude contrast of images of weak phase and amplitude objects can be strengthened almost twice as compared to standard light-pole contrast by means of shadow method of image formation without special contrasting of the objects. In spite of the contour effects (electron-microscopic attenuation) appearing at image formation by asymmetrical shadow method, the quantitative interpretation of such image is quite possible. The symmetrical shadow image (image with cone illumination) is more complexly realized than the asymmetric one, but it has some additional advantages. Particularly efficient suppression of background noises is there possible. Several symmetrical shadow images can be synthetized by the differential method with or without colour coding into the final image with the signal/noise ratio increased by an order.     

Microvoids in Bombyx mori silk. An electron microscope study.

The size and distribution of microvoids in Bombyx mori silk were examined by transmission electron microscopy of silver sulphide 'stained' filaments. Silver sulphide deposited in voids and accessible regions of molecular structure appears as dense particles in thin transverse and longitudinal sections of silk filaments. Small particles (about 8 nm or less in diameter) occur around or adjacent to the periphery of the filaments. Larger particles (around 10-15 nm in diameter) occur in the form of dendritic arrays in the core region of the filaments. The leading edges of the dendritic arrays are oriented towards the fibre periphery. The particles (microvoids) appear to be either spherical or rod-like in shape and are aligned parallel to the long axis of the filament. A skin/core structure is proposed.     

Identification of a phosphorus-containing storage granule in the cyanobacterium plectonema boryanum by electron microscope x-ray microanalysis.

Transmission electron microscopy of cyanobacteria couple with X-ray microanalysis has confirmed that dense deposits within these cells are composed of phosphorous.     

Correlation of x-ray deduced and experimental amino acid sequences of trimethylamine dehydrogenase.

The amino acid sequence of the iron-sulfur-flavoprotein, trimethylamine dehydrogenase, isolated from the bacterium W3A1 has been deduced from the x-ray diffraction pattern obtained at 2.4-A resolution. This sequence has been compared to portions of the primary sequence derived by gas-phase sequencing of isolated peptides obtained from cyanogen bromide and endoprotease Arg-C and Asp-N digestions of the purified enzyme. A consensus sequence has resulted and is comprised of 729 amino acids with Ala at both NH2- and COOH-terminal positions. The consensus sequence contains 13 cysteine residues. Approximately 80% of the sequence has been confirmed by direct sequencing with approximately 81% agreement with the x-ray deduced sequence. The calculated subunit molecular mass of the apoenzyme is 78,899 Da, in good agreement with published values of approximately 83,000. The anomalous scattering map from the native protein has also been shown to provide accurate information about the positions of most of the weak anomalous scattering centers such as sulfur or phosphorus atoms and to complement x-ray or chemical sequencing methods.     

An automated microscope for cytologic research a preliminary evaluation.

A research-oriented system for automated microscopy is described from an operational point of view. The system consists of a microscope, a TV camera, an automatic cell finder and a servo-driven computer controlled stage. The system is interfaced to a NOVA 840 computer having 112,000 words of 16-bit core memory and extensive peripherals. It is capable of performing a wide variety of image processing tasks and is being used to study various aspects of automated microscopy, with applications in, but not limited to, cytology. Results of preliminary performance evaluations are given.     

Small nuclear RNA localization during mitosis. An electron microscope study

The localization of small nuclear ribonucleic acids (snRNAs) during mitosis in Amoeba proteus was studied by high voltage (1,000 kV) electron microscope autoradiography. By suitable micromanipulations, the snRNA's, labeled with [3H]uridine, were made to be the only radioactive molecules in the cell and thus easy to follow autoradiographically. During interphase the snRNA label, which is almost exclusively nuclear, is distributed fairly uniformly through the nucleus with a slightly higher amount of label over chromatin than over nonchromatin areas. During prophase the snRNAs, which continue to be largely nuclear, become highly concentrated in the condensing chromosomes. At metapase, almost all of the snRNAs are cytoplasmic and essentially none are associated with the maximally condensed chromatin. Beginning in early anaphase, the snRNAs resume their association with the chromosomes, with the degree of association increasing throughout anaphase. Most of the snRNAs are back in the nuclei by telophase, but the intranuclear localization is hard to determine. We conclude that snRNAs have a great affinity for the partially condensed chromosomes of prophase and anaphase, but none for the maximally condensed chromosomes of metaphase. A minor amount of snRNA localizations in association with nucleoli and the nuclear envelope are also reported. On the basis of these findings a role of snRNAs in genetic "reprogramming" or chromosome organization is proposed.