The AXB and BXA set of recombinant inbred mouse strains

The recombinant inbred (RI) set of strains, AXB and BXA, derived from C57BL/6J and A/J, originally constructed and maintained at the University of California/San Diego, have been imported into The Jackson Laboratory and are now in the 29th to 59th generation of brother-sister matings. Genetic quality control testing with 45 proviral and 11 biochemical markers previously typed in this RI set indicated that five strains had been genetically contaminated sometime in the past, so these strains have been discarded. The correct and complete strain distribution patterns for 56 genetic markers are reported for the remaining RI strain set, which consists of 31 living strains and 8 extinct strains for which DNA is available. Two additional strains, AXB 12 and BXA 17, are living and may be added to the set pending further tests of genetic purity. The progenitors of this RI set differ in susceptibility to 27 infectious diseases as well as atherosclerosis, obesity, diabetes, cancer, cleft palate, and hydrocephalus. Thus, the AXB and BXA set of RI strains will be useful in the genetic analysis of several complex diseases.     

Partial purification,subunit structure and thermal stability of the photochemical reaction center of the thermophilic green bacterium Chloroflexus aurantiacus

Spectrally pure reaction center preparations from Chloroflexus aurantiacus have been obtained in a stable form; however, the product contained several contaminating polypeptides. The reaction center pigment molecules (probably three bacteriochlorophyll a and three bacteriopheophytin a molecules) are associated with two polypeptides (M_r = 30000 and 28000) in a reaction center complex of M_r = 52000. No carotenoid is present in the complex. These data together with previous spectral data suggest that the Chloroflexus reaction center represents a more primitive evolutionary form of the purple bacterial reaction center, and that it has little if any relationship to the green bacterial component. A reaction center preparation from Rhodopseudomonas sphaeroides R26 was fully denatured at 50°C while the Chloroflexus reaction center required higher temperatures (70–75°C) for complete denaturation. Thus, an intrinsic membrane protein of a photosynthetic thermophile has been demonstrated to have greater thermal stability than the equivalent component of a mesophile.     

Convenient,laboratory procedure for producing solid d-arabino-hexos-2-ulose (d-glucosone)

The production of solid d-arabino-hexos-2-ulose (d-glucosone) from d-glucose by use of an enzyme, pyranose-2-oxidase (EC 1.1.3.10), is described. The enzyme is extracted from the mycelia of Polyporus obtusus, partially purified, and then immobilized on activated CH-Sepharose 4B. The enzymic conversion of d-glucose into d-glucosone is simple and convenient, and provides a product free from residual d-glucose. Lyophilization of the filtered reaction-solution yields the product, solid d-glucosone. Assay methods have been developed for monitoring the enzymic reaction and evaluating the purity of the final product.     

Regulation of Tyrosyl-Transfer Ribonucleic Acid Synthetase in Bacillus subtilis

Derepression of tyrosyl-transfer ribonucleic acid synthetase in Bacillus subtilis was observed in strains grown with limiting tyrosine, but not in regulatory mutants derepressed in biosynthetic enzyme synthesis.     

In Vitro Studies of α-Carboxyl-3-Thienylmethyl Penicillin,a New Semisynthetic Penicillin

The activity of a new semisynthetic penicillin, α-carboxyl-3-thienylmethyl penicillin (BRL-2288) was determined against 535 clinical isolates of gram-negative bacilli, by using the tube dilution technique. Nearly 80% of isolates of Proteus spp. were inhibited by 3.12 μg or less of this antibiotic per ml. BRL-2288 was as active as ampicillin against Escherichia coli. It was slightly more active than carbenicillin or 6-(d-α-sulfoaminophenylacetamido)-penicillanic acid against Pseudomonas sp., with over half of the isolates being inhibited by 50 μg or less of BRL-2288 per ml. Isolates of Klebsiella sp. were routinely resistant to this antibiotic. The drug was bactericidal against most sensitive organisms. BRL-2288 was less active against large inocula. A strain of Pseudomonas sp. which developed resistance to carbenicillin also developed resistance to BRL-2288 simultaneously.     

Functional analysis of the antigenic structure of a minor T cell determinant from pigeon cytochrome C. Evidence against an alpha-helical conformation

A minor T cell determinant from pigeon cytochrome c, composed of residues 43 to 58 (p43-58), was synthesized along with a series of 48 analogs containing amino or carboxyl-terminal deletions or single amino acid substitutions. These peptides were analyzed functionally for their ability to elicit unique T cell populations on immunization of C57BL/10 mice and to stimulate a degenerate T cell clone capable of recognizing p43-58 in association with two different Ia molecules, A beta b:A alpha b and A beta d:A alpha d. These experiments allowed us to identify the residues in the determinant that are critical for T cell activation. Residues 50 and 52 had the dominant influence on T cell specificity, and residues 47, 48, 49, 51, and 53 had weak effects. Residues 46 and 54 were hardly recognized by the TCR at all, but appeared to influence the potency of the determinant by interacting with the Ia molecule. Finally, substitutions at positions 55 to 58 had no effect, but removal of these residues reduced the potency of the peptide, suggesting a contribution from the peptide backbone of this part of the molecule during T cell activation. An analysis of the spatial relationship of these dominant epitopic and agretopic residues suggests that this determinant does not assume a pure alpha-helical secondary structure when bound to the Ia molecule.     

Age-related differences in TGF-α and proto-oncogenes expression in rat liver after a low dose of carbon tetrachloride

The resiliency of rats during early postnatal development to CCl₄ or to an interactive hepatotoxicity of chlordecone (CD) + CCl₄ has been shown to be due to an efficient stimulation of tissue repair. The objective of the current study was to investigate if this is due to efficient expression of transforming growth factor-α (TGF-α) and proto-oncogenes. Postnatally developing (20 day old) and adult (60 day old) male Sprague–Dawley rats were challenged with a single low dose of CCl₄ (100 μL/kg, ip) or corn oil. Liver samples were collected during a time course (0–96 h) after the administration of CCl₄ and used to examine TGF-α and early (c-fos) and late (H-ras and K-ras) proto-oncogenes mRNA expressions. Significant increases in TGF-α, H-ras, and K-ras gene expressions were evident as early as 12 hours after CCl₄ and peaked between 24 and 48 hours in an age-dependent manner as detected by slot-blot analysis. Results of the study revealed three- and twofold increases in TGF-α gene expression in 20 and 60 day old rats, respectively, after CCl₄. There were 3.5- and 2.5-fold increases in H-ras and 4.4- and 3.4-fold increases in K-ras in 20 and 60 day old rats, respectively. In contrast, a 10-fold increase in c-fos mRNA expression was evident in 20 day old rats 1 hour after CCl₄ treatment, returning to the baseline value by 3 hours, whereas in 60 day old rats, this increase was less than twofold. The overall findings of this study indicate that TGF-α and the early and late proto-oncogene mRNA expressions were enhanced in an age- and time-dependent manner in response to a low dose of CCl₄. These results further strengthen the view that the remarkable resiliency of rats to hepatotoxicants during early postnatal development is due to substantial increases in stimulation of hepatocellular regeneration and tissue repair mechanisms, leading to regression of liver injury and recovery. © 1996 John Wiley & Sons, Inc.     

Individual differences in sensitivity to bitter-tasting substances

Perception of several bitter-tasting compounds was tested in52 subjects. Stable individual differences in the perceivedintensity of the bitterness of suprathreshold concentrationsof quinine sulfate (QSO₄) and urea were found. Whereas 18 subjectsjudged selected concentrations of these compounds to be equallybitter, 17 found QSO₄ to be more bitter than urea, and 17 foundurea to be more bitter than QSO₄. These reliable individualdifferences were significantly related to threshold sensitivityto QSO₄; that is, individuals who perceived QSO₄ to be moreintense than urea at suprathreshold concentrations also hadlower QSO₄ thresholds than did those who perceived urea to bemore intense than QSO₄. There appeared to be no relationshipbetween the relative perceived intensities of these compoundsand rating of the bitterness of PROP (6-n-propylthiouracil).However, QSO₄-sensitive individuals tended to find the bitternessof suprathreshold caffeine and sucrose octaacetate to be greaterthan that of suprathreshold magnesium sulfate, whereas the reversewas true for urea-sensitive individuals. This pattern parallelsthe pattern of cross-adaptation among these compounds reportedby other investigators. These results are consistent with theexistence of multiple bitter transduction sequences and suggestthat individual differences in response to various bitter compoundsmay reflect differences in teh relative availability of specifictransduction sequences.     

Murine FGF-4 gene expression is spatially restricted within embryonic skeletal muscle and other tissues

Fibroblast growth factors are believed to play many distinct roles in vertebrate development, owing to their ability to stimulate cell growth, prevent cell death, determine cell fate, and inhibit terminal differentiation in a variety of in vitro culture systems. We have used in situ hybridization to localize fibroblast growth factor-4 (FGF-4, also termed HST and K-FGF) gene expression in 7.5 to 16.5 day gestation mouse embryos. Seven discrete sites of gene expression were detected: (1) primitive streak (E7.5–8.5); (2) paraxial presomitic mesoderm in the trunk (E7.5–11.5); (3) primitive neuroectoderm (E8.0–8.5); (4) pharyngeal pouch endoderm (E8.5–9.5); (5) branchial arch ectoderm (E8.5–9.5); (6) limb apical ectoderm (E10.5–12.5), and (7) skeletal myoblast groups (E9.5–13.5). FGF-4 gene expression is spatially restricted within many of these sites. The profile of FGF-4 gene expression among skeletal muscle groups is overlapping, but distinct, from that of FGF-5, thereby revealing myoblast heterogeneity at the molecular level and suggesting distinct roles for multiple FGFs in muscle development.