The structure and properties of histone F2a comprising the heterologous group F2a1 and F2a2 studied by 13C nuclear magnetic resonance

¹³C n.m.r. spectra have been obtained for aqueous solutions of histones F2a₁ and F2a₂, for the group F2a, for the appropriate amino acid mixturesand for the corresponding hydrolysates. These, when compared with computer simulated spectra give good agreement for secondary structure with that calculated from the known primary structure of the proteins. Evidence based on the spectra obtained at various salt concentrations leads to the conclusion that F2a is not a simple mixture but an interacting heterologous group of histones F2a₁ and F2a₂.     

Molecular architecture of adult locust cuticle at the electron microscope level

It is shown that locust adult endocuticle consists of a daily alternation of two types of chitin-protein architecture: (i) non-lamellate day layers with microfibrils oriented in a preferred direction, traversed by pore canals whose shape resembles an untwisted ribbon, (ii) lamellate night layers with helicoidally oriented microfibrils traversed by pore canals shaped like regularly twisted ribbons. Uncoupling the circadian clock which normally controls the timing of these two types leads to growth of cuticles which are organized like one or the other throughout. We can thus experimentally change the architecture of the microfibrils which in turn changes the pore canals.     

Anesthesiology: glucose administration during neurosurgical procedures

The Scientific Board of the California Medical Association presents the following inventory of items of progress in anesthesiology. Each item, in the judgment of a panel of knowledgeable physicians, has recently become reasonably firmly established, both as to scientific fact and important clinical significance. The items are presented in simple epitome and an authoritative reference, both to the item itself and to the subject as a whole, is generally given for those who may be unfamiliar with a particular item. The purpose is to assist busy practitioners, students, research workers, or scholars to stay abreast of these items of progress in anesthesiology that have recently achieved a substantial degree of authoritative acceptance, whether in their own field of special interest or another.The items of progress listed below were selected by the Advisory Panel to the Section on Anesthesiology of the California Medical Association, and the summaries were prepared under its direction.     

The sperm structure of the gall-midges Anaretella and Lestremia (Insecta, Diptera, Cecidomyiidae)

The sperm structure of some dipteran flies belonging to the Lestremiini tribe have been examined. Anaretella cincta was shown to have an axoneme made of 20-21 microtubular doublets, disposed in a circle in a cross section and surrounding a mitochondrion. Other crystal-containing mitochondria flank the axoneme; a second species (Anaretella sp.) was provided with 21-22 axonemal doublets. Lestremia is characterized by a flattened axoneme, consisting of about 150 doublets arranged in 2 antiparallel rows and surrounding a few mitochondria. These mitochondria, in Lestremia sp., have a crystalline core that is missing in Lestremia cinerea. The structure of microtubular doublets is quite similar in the 2 related genera and a derivation of the flattened axoneme found in Lestremia from that circular of Anaretella is suggested. Sperm structure suggests that Lestremia cinerea is not a uniform species.     

Specificity and Photomorphogenic Nature of Ultraviolet-B-Induced Cotyledon Curling in Brassica napus L

Three general classes of photomorphogenic photoreceptors have been characterized in higher plants: phytochrome, a blue light/ultraviolet (UV)-A photoreceptor(s), and a UV-B sensory system(s). Although a great deal is known about phytochrome and the blue light/UV-A photoreceptor(s), little is known about UV-B detection processes. One reason for this is the lack of readily quantifiable morphogenic responses that are specifically induced by UV-B radiation. We have discovered a response to UV-B, upward curling of Brassica napus L. cotyledons, that may be useful for probing the mechanism of UV-B photoreception. The process was initially observed when B. napus seeds were germinated under visible light plus UV-B radiation, but did not occur under visible light alone or visible light plus UV-A. When 5-d-old seedlings grown in visible light were given relatively short exposures of UV-B (100 min of 5.5 [mu]mol m-2 s-1), the curling response was also observed. Development of curling was separated from the application of this UV-B pulse by a 14-h latent period. Pulses of red light, blue light, farred light, and UV-A (100 min of 5.5 [mu]mol m-2 s-1) did not induce curling, indicating UV-B specificity Additionally, these other spectral regions did not reverse or enhance the UV-B-triggered response. The degree of curling showed a log-linear dependence on UV-B fluence (6-40 mmol m-2) and reciprocity with respect to length of exposure and fluence rate. The data indicate that curling is photomorphogenic in nature and may be triggered by a single photoreceptor species.     

DNA Damage Levels Determine Cyclobutyl Pyrimidine Dimer Repair Mechanisms in Alfalfa Seedlings

Ultraviolet radiation in sunlight damages DNA in plants, but little is understood about the types, lesion capacity, and coordination of repair pathways. We challenged intact alfalfa seedlings with UV doses that induced different initial levels of cyclobutyl pyrimidine dimers and measured repair by excision and photoreactivation. By using alkaline gel electrophoresis of nonradioactive DNAs treated with a cyclobutyl pyrimidine dimer-specific UV endonuclease, we quantitated ethidium-stained DNA by electronic imaging and calculated lesion frequencies from the number average molecular lengths. At low initial dimer frequencies (less than ~30 dimers per million bases), the seedlings used only photoreactivation to repair dimers; excision repair was not significant. At higher damage levels, both excision and photorepair contributed significantly. This strategy would allow plants with low damage levels to use error-free repair requiring only an external light energy source, whereas seedlings subjected to higher damage frequencies could call on additional repair processes requiring cellular energy. Characterization of repair in plants thus requires an investigation of a range of conditions, including the level of initial damage.