DNA rearrangement causes a high rate of spontaneous mutation at the immunoglobulin heavy-chain locus of a mouse myeloma cell line

The spontaneous mutation rate of immunoglobulin genes expressed in myeloma cells is well above that of other genes expressed in these or in other cell types. The nature of such mutations in one myeloma cell line, MPC11, was explored at the molecular level. Included in this study were MPC11 variants representing 24 independent and spontaneous mutations affecting immunoglobulin secretion. Of the mutants studied, 19 had ceased immunoglobulin heavy chain (IgH) production (nonproducers), and 5 produced from as little as 1/1,000 to as much as 1/10 the amount of immunoglobulin produced by MPC11 (low producers). Only one of the MPC11 mutants (a nonproducer) showed no evidence of DNA rearrangement in or near the expressed IgH gene. The formerly expressed gamma 2b gene had been deleted in 18 of the 19 nonproducers. All of the low producers had undergone DNA rearrangement in or near the expressed IgH gene, and three of them produced immunoglobulin of a new heavy chain class. The cause for reduced heavy-chain synthesis in the low producers is not yet known. However, in several of these mutants, the defect appeared to be posttranscriptional. In these cell lines, steady-state IgH mRNA levels were much lower than in the parent cell line, while the heavy-chain gene transcription rate remained unchanged.

RNA sequence containing hexanucleotide AAUAAA directs efficient mRNA polyadenylation in vitro

To determine whether a specific nucleotide sequence is required to direct polyadenylation of a simian virus 40 early pre-mRNA in a soluble HeLa whole-cell lysate, we constructed a series of rearranged and deleted DNA templates, transcribed them in vitro, and determined whether the resultant RNAs could be polyadenylated when incubated in whole-cell lysate. When a 237-base-pair DNA fragment encoding the 3' end of the simian virus 40 early pre-mRNA was transferred to recombinant plasmids encoding RNAs that were not substrates for polyadenylation, the resultant RNAs could now be polyadenylated efficiently. In one case, the chimeric RNA was polyadenylated even more efficiently than was the original simian virus 40 early transcript. Analysis of the RNAs produced from the deletion mutant templates revealed that only RNAs containing at least one copy of the AAUAAA sequence situated near the 3' end and implicated in 3'-end formation and polyadenylation in vivo could be polyadenylated in vitro. Surprisingly, this sequence directed polyadenylation of pre-mRNAs not only when near the RNA 3' end, i.e., 50 nucleotides or less away, but also when the 3' end was situated over 400 nucleotides downstream. Thus, our results show that a polyadenylic acid polymerase activity in HeLa lysates can recognize a specific nucleotide sequence in pre-mRNA and then, in the absence of the nucleolytic cleavage that presumably occurs in vivo, locate the RNA 3' end and use it as a primer for polyadenylic acid synthesis.

Fever and proximal tubular function in acute pyelonephritis

The urinary excretion of alpha 1-microglobulin (alpha 1M), beta 2-microglobulin (beta 2M), retinol-binding protein (RBP) and N-acetyl-beta-D-glucosaminidase (NAG) as markers of proximal tubular dysfunction was measured in various forms of urinary tract infections (UTI) and in fever due to non-renal infections. The urinary concentration of these proteins was significantly increased in acute pyelonephritis compared with acute cystitis and asymptomatic bacteriuria. Tubular proteinuria and enzymuria could also be demonstrated in subjects with fever of non-renal origin and corresponded to the findings of pyelonephritis. It is suggested that fever per se is the most likely cause of the tubular proteinuria seen in acute pyelonephritis. In localizing an acute UTI characterization of the urinary protein profile seems to have no advantage over a carefully measured body temperature. The urinary excretion of alpha 1M,beta 2M and RBP were highly correlated, while urinary NAG activity was less correlated to these low-molecular weight proteins. Fibrin degradation product D (FDP-D) was detected in the urines in 60% of the patients with acute pyelonephritis and in one third of those with acute cystitis. The estimation of FDP in urine therefore seems to be of little value in the level diagnosis of UTI.

Black thyroid: clinical manifestations, ultrastructural findings, and possible mechanisms

Ultrastructural examination of three black thyroid glands showed lysosomal accumulations of lipofuscin-like pigment and granular electron-dense material in association with 1) a minocycline-associated black thyroid with normal thyroid function; 2) a minocycline-associated black thyroid with a significant inflammatory component, fibrosis, and primary hypothyroidism; and 3) a black thyroid gland with no exposure to minocycline. The deposition of the pigments in the three cases resulted in macroscopically recognizable black thyroid glands. It is speculated that an imbalance in lysosomal function accounts for this abnormality. The glandular hypofunction documented in case 2 is unique and confirms the need to monitor function carefully in patients who are receiving minocycline. In one case electrondense deposits were identified in the thyroid gland interstitium.

Cluster analysis of chromatographic profiles of urine proteins

A method to examine and classify the chromatograms of urinary proteins, separated on a fast protein liquid chromatography system, is presented. For the analyses a measure of similarity between chromatogram profiles is defined and this is used to implement a statistical cluster analysis technique for the identification of a system of classification. The resulting classification can be related to a clinical assessment of the proteinuria of the sample urines, which are from patients with various renal disorders.

Renal proximal dysfunction in patients with rheumatic diseases

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Osmotic deformation of red blood cell ghosts induced by carbohydrates

The osmotic response of bovine red blood cell ghosts to a series of sugars is studied by light scattering. The sealed and right-side-out ghosts are prepared by the procedure of Steck and Kant (Steck, T.L. and Kant, J.A. (1974) Methods Enzymol. 31, 172-180), swollen in a hypotonic phosphate-buffered saline solution and their size and shape determined by elastic and quasielastic light scattering. Different carbohydrates are then added to the suspending medium in order to examine the osmotic responses, and the osmotic deformation of ghosts is shown to be spherically symmetric. Having thus established the deformation behavior, we then rank the osmotic activity of a carbohydrate relative to a standard, i.e., raffinose. It is found that the osmotic response of the ghosts to sucrose is about the same as that to raffinose, and the response to the smaller carbohydrates simply follows the number of carbons in various sugars; glucose and fractose are about 1.7 times less effective than raffinose, and pentaerythritol and meso-erythritol are 2.3 times less effective. Glyceraldehyde, which is 3.6 times less effective than raffinose, is the least effective sugar analog among those that we have tested.

Urinary protein profiles after burn injury

A study of the change of urinary protein excretion has been made in 26 patients followed from the time of admission to time of discharge from the Yorkshire Regional Burn Centre (7-200 days). Total protein, IgG and albumin (as indicators of glomerular function) and alpha 1-microglobulin, beta 2-microglobulin, retinol binding protein and N-acetyl-beta-D-glucosaminidase (as indicators of proximal tubular function) as well as the patterns on SDS polyacrylamide gel electrophoresis were examined. Patients were divided into three groups according to their urinary protein profiles. The first group was 3 patients who showed little or no evidence of proteinuria; the second group consisted of 7 patients who showed a mild and transient tubular proteinuria, all of whom recovered normal function within one week. The third group, 16 patients, developed moderate to severe proteinuria usually started as a mixed pattern of glomerular and tubular proteinuria, characterized by the excretion of a high level of total protein. After a few days, this pattern changed to a typical tubular proteinuria and the latter could last for as long as 200 days; in some of these patients a secondary increase of low molecular weight protein excretion occurred either due to a latent renal complication or induced by the administration of aminoglycosides. There is a close correlation between the intensity and patterns of the proteinuria and the severity and clinical progress of the burn.

Alpha-1-microglobulin: an indicator protein for renal tubular function

A comparison of urinary alpha 1-microglobulin concentrations to the behaviour of other indicators of renal tubular disorders, beta 2-microglobulin, retinol-binding protein and N-acetyl-beta-D-glucosaminidase (NAG) has been made. In acute tubular disorders the concentrations of urinary beta 2M and RBP are highly correlated (r = 0.89) but this is less marked for alpha 1M and beta 2M (r = 0.55) and alpha 1M and RBP r = 0.48. NAG tends to run a parallel course to alpha 1M concentrations but lags behind the recovery of low molecular weight protein reabsorption following injury of the tubular cells. The concentrations of alpha 1M, and in particular its stability at low pH suggest that this protein may be useful in screening for tubular abnormalities and detecting chronic asymptomatic renal tubular dysfunction. Urinary alpha 1M greater than 15 mg/g creatinine is strongly suspicious of a proximal tubular dysfunction. The distinction between pure tubular proteinuria and mixed glomerular and tubular proteinuria requires further analysis.

Aggregation equilibria of Escherichia coli RNA polymerase: evidence for anion-linked conformational transitions in the protomers of core and holoenzyme

The aggregation equilibria of Escherichia coli RNA polymerase core and holoenzyme have been studied by velocity sedimentation as a function of [NaCl] both in the presence and in the absence of MgCl2. Effects of other anions (F- and I-), pH, and temperature have also been examined. Diffusion coefficients obtained by quasi-elastic light scattering (QLS) at high and low salt concentrations were used in conjunction with sedimentation coefficients under these conditions to obtain molecular weights of the protomer and aggregates of the core enzyme. At low salt concentration, core aggregates to a tetramer in the absence of MgCl2 and to an octamer in the presence of MgCl2. Some ambiguity exists in the interpretation of the sedimentation and QLS data for holoenzyme. The sedimentation results are consistent with the formation of dimers at low salt, both in the presence and in the absence of MgCl2. In all cases, equilibrium constants were calculated assuming a simple monomer--j-mer stoichiometry. These equilibrium constants are extremely sensitive functions of the concentration and type of monovalent anion. In Cl-, aggregation of both core and holoenzyme begins abruptly when the salt concentration is reduced below approximately 0.2 M (at a protein concentration of approximately 0.30 mg/mL); for core, substitution of I- for Cl- suppresses aggregation while F- enhances aggregation at a fixed anion concentration. No specific effect of monovalent cations (Na+, NH4+) is observed; Mg2+ has no effect on holoenzyme dimerization and has little effect on the salt range of core aggregation, though the stoichiometries of the core aggregates in the presence and absence of Mg2+ differ. Anion effects on these equilibria were modeled by assuming that a class of anion-binding sites on the protomer is not present in the aggregate, so that anion release accompanies aggregation. Analytical expressions for several models of the effect of anions on the aggregation equilibria were derived by using the method of binding polynomials. The salt dependence of the aggregation equilibria in the absence of Mg2+ appears inconsistent with a model in which the anion-binding sites on the protomer are independent (noncooperative), but it is well described by a model in which anion binding to the protomers occurs in a completely cooperative manner. The molecular basis of this apparent cooperative effect of anions on the aggregation equilibria is proposed to be an allosteric effect of anions on conformational equilibria of the protomers of core polymerase and the holoenzyme. Implications of such a salt-dependent conformational transition for the DNA-binding interactions of the enzyme are considered.

Electric and optical anisotropy and their osmotically induced changes of photoreceptor disk membrane vesicles

Electro-optical characterization of the photoreceptor disk membrane vesicle is performed by examining the electric field and concentration dependence of the study-state birefringence of aqueous suspensions of the vesicles. The electric polarizability anisotropy is found to be negative and of large magnitude: alpha 1 - alpha 2 = -(1-3) X 10 cm3. The optical anisotropy is determined to be also negative but of small magnitude: g 1 - g 2 = -1 X 10(-7). The specific Kerr constant deduced from the concentration dependence of the Kerr constant is found to be very large: Ksp = 7 X 10(-4) e.s.u. Upon deforming the vesicles osmotically from the spherical shell to the disk structure, the steady-state birefringence increases by an order of magnitude which is attributed solely to the increase in optical anisotropy attending the corresponding change in the geometric eccentricity of the vesicle. A plausible birefringence mechanism based on the known structural features of the vesicles is proposed, which would account for these findings.

Lateral diffusion of photopigments in photoreceptor disk membrane vesicles by the dynamic Kerr effect

The lateral diffusion of photopigment molecules in the photoreceptor disk membranes, osmotically swollen into spherical vesicles, has been investigated by dynamic Kerr effect measurements. Upon application of a rapidly reversing bipolar electric field to dilute aqueous suspensions of bovine disk membrane vesicles, the birefringence transient shows a characteristic rise and a deep dip corresponding to the first and second pulses, respectively. The birefringence transient is ascribed to the slowly induced dipole moment caused by electric field induced displacement of the photopigment distribution on the vesicular surface. The lateral translational diffusion coefficient is estimated from the time constant of the slowly induced dipole as D = (3.3 +/- 1.2) X 10(-9) cm2 s-1. When spermine, a cationic tetraamine, is bound to the disk membrane vesicles, the relaxation time of the slowly induced dipole is shown to become longer, indicating that the birefringence mechanism is indeed due to the field-induced photopigment displacement.

Permeability to ions of bovine retinal disk membrane vesicles in the bleached state

The permeability of the bleached disk membrane of retinal rod outer segments to univalent and divalent ions is studied by light scattering. The membranes are isolated from frozen dark-adapted bovine retinae, swollen into spherical vesicles in a hypotonic medium and bleached in dilute suspension and their size is determined by elastic and quasi-elastic light scatterings. Various electrolytes are then added to the suspending medium in order to examine their osmotic activity relative to the vesicles deformation characteristics. By following the deformation behavior of the membrane vesicles by elastic light scattering in terms of the oblate ellipsoidal shell model, the osmotic activity of a given electrolyte is qualitatively deduced and thereby the permeability of the membrane to the electrolyte is ranked in reference to a chosen standard, i.e., sucrose. By this method, we show that the permeabilities to Na+, K+, Mg2+ and Ca2+ are all alike, and those to halides (F-, Cl-, Br-, I-), nitrate and phosphates (HPO4(2-)/H2PO4-) are similar. Acetate, however, is about 3-times more permeative, while sulfate is less permeative than the other anions by about the same factor. The viability of our method is checked with use of an ionophore, lasolocid (X-537A), by establishing partial recovery from the osmotic deformation through the suppression of the cation osmotic effect. Ion-induced aggregation and pH-dependent size and shape changes are both found to be insignificant.