The absorption of phosphate from the digestive tract of ruminant animals

The late competence protein ComF1 is required for genetic transformation in Bacillus subtilis. Because of the sequence similarities of ComF1 to known ATP-dependent DNA helicases and translocases, we have hypothesized that this protein either unwinds bound double-stranded DNA or helps in the translocation of the transforming single-stranded DNA across the cell membrane. Two important implications of this hypothesis (the association of ComF1 with the membrane and its specific requirement for DNA uptake) have been tested in this report. Using cell fractionation techniques and Western blotting analysis, we show that ComF1 is located almost exclusively on the cell membrane and that it is membrane-targeted independently of other competence proteins. Moreover, ComF1 behaves like an integral membrane protein in extractability and detergent partition assays. We also show that this protein is required for the DNA-uptake step during transformation but not for DNA binding to the cell surface. DNA uptake is blocked in strains with null mutations or in-frame deletions in comF1 but also in strains that overproduce the ComF1 protein under competence conditions. This last observation suggests that ComF1 expression must be balanced with that of other competence proteins, with which it may interact to form a multisubunit complex for DNA uptake.     

Imaging of calcaneal fractures

The radiologic evaluation of injuries to the calcaneus begins with plain x-rays. The addition of special views may be necessary as part of the preliminary evaluation to assist in the diagnosis or in further delineating the extent of the fracture. CT scanning is generally required for preoperative planning when there is extensive comminution and/or intra-articular involvement. MRI has a limited role in the treatment of calcaneus fractures.     

Changing echocardiography request patterns between 1988 and 1993

OBJECTIVES: This article evaluates the concept of auditory threshold and discusses the limitations of assessing threshold in human neonates. The advantages and limitations of assessing neonatal threshold by means of auditory brain stem response (ABR) are discussed, and data from several studies of newborn ABR threshold are compared. The authors report data from their own study designed to compare adult and neonatal ABR threshold using tonal stimuli. EXPERIMENTAL DESIGN: Several studies are compared. Data from the authors are ABR thresholds for tone bursts of 0.5, 1.5, 4, and 8 kHz, determined from 2-channel recordings in full-term neonates and adults. Stimuli were calibrated in SPL by means of a probe microphone inserted into the ear canal along with the insert transducer of each subject. RESULTS: All studies find a degree of threshold elevation in neonates relative to adult threshold. Neonatal ABR thresholds from our laboratory for stimuli from 500 through 8000 Hz are elevated relative to adult thresholds by 5 to 25 dB. Threshold elevation in our data and in other studies has found that neonatal ABR thresholds to high-frequency stimuli show the largest elevation relative to adults and low-frequency stimuli the most mature. CONCLUSIONS: Thresholds of neonates, as measured by the ABR, are immature especially for high-frequency stimuli. Proper stimulus calibrations, which removes the influence of ear canal resonance, are important for comparisons of data across age groups. Developmental differences in the conductive mechanism and neural immaturity are the most harmonious explanations for elevation of neonatal ABR thresholds.     

Progress in pediatric liver transplantation--the Birmingham experience

This report describes the evolution of the Birmingham, UK experience with pediatric liver transplantation from 1983 to present. Two hundred liver grafts were placed in 168 children less than 17 years of age. The current survival rate exceeds 80%.     

Oligomerization of expanded-polyglutamine domain fluorescent fusion proteins in cultured mammalian cells

Six inherited neurologic diseases, including Huntington's disease, result from the expansion of a CAG domain of the disease genes to produce a domain of more than 40 glutamines in the expressed protein. The mechanism by which expansion of this polyglutamine domain causes disease is unknown. Recent studies demonstrated oligomerization of polyglutamine-domain proteins in mammalian neurons. To study oligomerization of polyglutamine proteins and to identify heterologous protein interactions, varying length polyglutamine-green fluorescent protein fusion proteins were expressed in cultured COS-7 cells. The 19- and 35-glutamine fusion proteins (non-pathologic length) distributed diffusely throughout the cytoplasm. In contrast, 56- and 80-glutamine fusion proteins (pathologic length) formed fibrillar arrays resembling those previously observed in neurons in Huntington's disease and in a transgenic mouse model. These aggregates were intranuclear and intracytoplasmic. Intracytoplasmic aggregates were surrounded by collapsed intermediate filaments. The intermediate filament protein vimentin co-immunoisolated with expanded polyglutamine fusion proteins. This cellular model will expedite investigations into oligomerization of polyglutamine proteins and their interactions with other proteins.     

A transposable partitioning locus used to stabilize plasmid-borne hydrogen oxidation and trifolitoxin production genes in a Sinorhizobium strain

Improved nitrogen-fixing inoculum strains for leguminous crops must be able to effectively compete with indigenous strains for nodulation, enhance legume productivity compared to the productivity obtained with indigenous strains, and maintain stable expression of any added genes in the absence of selection pressure. We constructed a transposable element containing the tfx region for expression of increased nodulation competitiveness and the par locus for plasmid stability. The transposon was inserted into tetA of pHU52, a broad-host-range plasmid conferring the H2 uptake phenotype. The resulting plasmid, pHUTFXPAR, conferred the plasmid stability, trifolitoxin production, and H2 uptake phenotypes in the broad-host-range organism Sinorhizobium sp. strain ANU280. The broad applications of a transposon conferring plasmid stability are discussed.     

The gas trophicity of pathogenic bacteria]

Yersinia pseudotuberculosis and Listeria have been shown to be capable of assimilating carbon dioxide from the air and using its carbon for the synthesis of biopolymers of the bacterial cell. These microorganisms, the causative agents of saprozoonotic infections, have also been found to be capable of assimilating molecular nitrogen from the air in small amounts. The data on the influence of the growth conditions of the cultures (hydrogen concentration, the presence of carbon dioxide and oxygen, temperature) on the activity of acetylene reduction by microbial cells. At low temperature molecular nitrogen is fixed by Listeria twice as actively as by Y.pseudotuberculosis. Not all bacterial strains under study have been found to be capable of acetylene reduction. The presence of fixed nitrogen in the medium suppresses the process of the reduction of acetylene into ethylene.     

Quantitative freeze-fracture analysis of the frog neuromuscular junction synapse--II. Proximal-distal measurements

Neurotransmitter release from different parts of frog motor nerve terminals is often non-uniform. There is a decrease in release efficacy from the distal regions of frog motor nerve terminal branches. Since release is thought to occur near the double arrays of large intramembranous particles that constitute the pre-synaptic active zones (AZs), we have examined quantitatively the proximal-distal distribution of AZ structure, using a novel freeze-fracture technique that produces replicas of large fractions of terminals, including the region of nerve entry. This enables us to know the proximal distal orientation of each branch. From 23 end-plates we have obtained fractures of 72 branches. For 27 of these branches we have obtained continuous fractures both greater than 25 microm in length and with sufficient information to determine their proximal distal polarity. Only a few of these branches showed a marked distal decrease in AZ length/unit length of terminal, while several junctions had short regions (5-10 microm), either proximally or distally, that exhibited amounts of AZ that were substantially greater or smaller than the mean value for that terminal branch. The terminal area, post-synaptic gutter width and nerve terminal width all exhibit some distal decline concomitant with the distal tapering of nerve terminal branches. AZ length tends to have the least decline compared to the other parameters. Thus, the vast majority of frog motor nerve terminal branches do not display a significant proximal-distal gradient in the amount of AZ structure / microm terminal length. The present data do not provide an obvious ultrastructural correlate for the distal decline in transmitter release that some authors have observed.