Knockdown of Tlr3 in dorsal striatum reduces ethanol consumption and acute functional tolerance in male mice

Systemic activation of toll-like receptor 3 (TLR3) signaling using poly(I:C), a TLR3 agonist, drives ethanol consumption in several rodent models, while global knockout of Tlr3 reduces drinking in C57BL/6J male mice. To determine if brain TLR3 pathways are involved in drinking behavior, we used CRISPR/Cas9 genome editing to generate a Tlr3 floxed (Tlr3F/F) mouse line. After sequence confirmation and functional validation of Tlr3 brain transcripts, we injected Tlr3F/F male mice with an adeno-associated virus expressing Cre recombinase (AAV5-CMV-Cre-GFP) to knockdown Tlr3 in the medial prefrontal cortex, nucleus accumbens, or dorsal striatum (DS). Only Tlr3 knockdown in the DS decreased two-bottle choice, every-other-day (2BC-EOD) ethanol consumption. DS-specific deletion of Tlr3 also increased intoxication and prevented acute functional tolerance to ethanol. In contrast, poly(I:C)-induced activation of TLR3 signaling decreased intoxication in male C57BL/6J mice, consistent with its ability to increase 2BC-EOD ethanol consumption in these mice. We also found that TLR3 was highly colocalized with DS neurons. AAV5-Cre transfection occurred predominantly in neurons, but there was minimal transfection in astrocytes and microglia. Collectively, our previous and current studies show that activating or inhibiting TLR3 signaling produces opposite effects on acute responses to ethanol and on ethanol consumption. While previous studies, however, used global knockout or systemic TLR3 activation (which alter peripheral and brain innate immune responses), the current results provide new evidence that brain TLR3 signaling regulates ethanol drinking. We propose that activation of TLR3 signaling in DS neurons increases ethanol consumption and that a striatal TLR3 pathway is a potential target to reduce excessive drinking.

Brain-specific serine/threonine-protein kinase 1 is a substrate of protein kinase C epsilon involved in sex-specific ethanol and anxiety phenotypes

Protein kinase C epsilon (PKCε) regulates behavioural responses to ethanol and plays a role in anxiety-like behaviour, but knowledge is limited on downstream substrates of PKCε that contribute to these behaviours. We recently identified brain-specific serine/threonine-protein kinase 1 (BRSK1) as a substrate of PKCε. Here, we test the hypothesis that BRSK1 mediates responses to ethanol and anxiety-like behaviours that are also PKCε dependent. We used in vitro kinase assays to further validate BRSK1 as a substrate of PKCε and used Brsk1-/- mice to assess the role of BRSK1 in ethanol- and anxiety-related behaviours and in physiological responses to ethanol. We found that BRSK1 is phosphorylated by PKCε at a residue identified in a chemical genetic screen of PKCε substrates in mouse brain. Like Prkce-/- mice, male and female Brsk1-/- mice were more sensitive than wild-type to the acute sedative-hypnotic effect of alcohol. Unlike Prkce-/- mice, Brsk1-/- mice responded like wild-type to ataxic doses of ethanol. Although in Prkce-/- mice ethanol consumption and reward are reduced in both sexes, they were reduced only in female Brsk1-/- mice. Ex vivo slice electrophysiology revealed that ethanol-induced facilitation of GABA release in the central amygdala was absent in male Brsk1-/- mice similar to findings in male Prkce-/- mice. Collectively, these results indicate that BRSK1 is a target of PKCε that mediates some PKCε-dependent responses to ethanol in a sex-specific manner and plays a role distinct from PKCε in anxiety-like behaviour.

Proton resonance frequency chemical shift thermometry: experimental design and validation toward high-resolution noninvasive temperature monitoring and in vivo experience in a nonhuman primate model of acute ischemic stroke

BACKGROUND AND PURPOSE

Applications for noninvasive biologic temperature monitoring are widespread in biomedicine and of particular interest in the context of brain temperature regulation, where traditionally costly and invasive monitoring schemes limit their applicability in many settings. Brain thermal regulation, therefore, remains controversial, motivating the development of noninvasive approaches such as temperature-sensitive nuclear MR phenomena. The purpose of this work was to compare the utility of competing approaches to MR thermometry by using proton resonance frequency chemical shift. We tested 3 methodologies, hypothesizing the feasibility of a fast and accurate approach to chemical shift thermometry, in a phantom study at 3T.

MATERIALS AND METHODS

A conventional, paired approach (difference [DIFF]-1), an accelerated single-scan approach (DIFF-2), and a new, further accelerated strategy (DIFF-3) were tested. Phantom temperatures were modulated during real-time fiber optic temperature monitoring, with MR thermometry derived simultaneously from temperature-sensitive changes in the water proton chemical shift (∼0.01 ppm/°C). MR thermometry was subsequently performed in a series of in vivo nonhuman primate experiments under physiologic and ischemic conditions, testing its reproducibility and overall performance.

RESULTS

Chemical shift thermometry demonstrated excellent agreement with phantom temperatures for all 3 approaches (DIFF-1: linear regression R(2) = 0.994; P < .001; acquisition time = 4 minutes 40 seconds; DIFF-2: R(2) = 0.996; P < .001; acquisition time = 4 minutes; DIFF-3: R(2) = 0.998; P < .001; acquisition time = 40 seconds).

CONCLUSIONS

These findings confirm the comparability in performance of 3 competing approaches to MR thermometry and present in vivo applications under physiologic and ischemic conditions in a primate stroke model.

Allergen content of grass pollen preparations for skin prick testing and sublingual immunotherapy

BACKGROUND

The allergen content of diagnostics and immunotherapeutics is crucial for effective diagnosis and treatment. The aim of this study was to quantify and compare the allergen content of different grass pollen preparations for skin prick testing and sublingual immunotherapy (SLIT).

METHODS

Five skin prick test (SPT) solutions and 10 sublingual immunotherapeutics were analysed for protein and allergen concentration by Bradford assay, inhibition of IgE-binding to Phleum pratense ImmunoCAPs and content of the main allergen Phl p 5 by two-site enzyme immunoassay. In addition, the grass pollen preparations were compared by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting analyses.

RESULTS

Protein concentrations of SPT solutions ranged from 15 to 427 microg/ml, and Phl p 5 concentrations ranged from 0.15 to 18.3 microg/ml. The ranking of SPT solutions concerning Phl p 5 content and IgE inhibition capacity was the same, and the ranking of protein and allergen content was closely correlated (r = 0.9). Protein content of the maintenance doses of the immunotheurapeutics ranged from 5 to 153 microg, Phl p 5 content ranged from 0.2 to 21.6 microg. IgE inhibition capacity of the maintenance doses was closely correlated to their Phl p 5 and protein content. SDS-PAGE and immunoblots confirmed the differences in protein and allergen content.

CONCLUSIONS

Grass pollen preparations for SPT and SLIT varied greatly concerning protein and allergen content. Whereas this result corresponds to previous analyses results of SPT solutions, it was the first comparison of grass pollen immunotherapeutics. For diagnosis and therapy, these differences should be taken into account.

Defective human T-cell leukaemia virus type 1 (HTLV-1) genomes: no evidence in serologically indeterminate german blood donors but new type detected in established cell lines

Individuals reactive in antibody screening tests (ELISA) and with one or more reactions to HTLV-1 proteins on Western blotting, but lacking the criteria of a confirmed HTLV infection, are not exceptional in regions with a low prevalence of HTLV-1/-2 infections. PCR analysis of these indeterminate samples, using "diagnostic" pol and tax sets of primers, give negative results. However, expression of HTLV-1 defective proviruses with internal deletions undetectable by PCR with diagnostic primers could have taken place. Seven German HTLV-1 ELISA-reactive blood donors, who showed reactivity also in Western blots against several viral proteins, and twenty haemophiliacs, were examined by nested PCR and/or PCR/Southern hybridisation with primers designed for detection of HTLV-1 defective proviruses. No HTLV-1-specific amplification products were obtained. However, HTLV-1 defective proviruses with large internal deletions were detected in four out of five cell lines established from symptomatic HTLV-1 cases and two in HUT-102 cells. In two amplicons, short inverted rRNA sequences between gag and env fragments of HTLV-1 defective proviruses were revealed. These results do not exclude the presence of defective HTLV-1 proviruses in individuals with indeterminate serology although this is unlikely.

Evaluation of a multidimensional solid-phase extraction platform for highly selective on-line cleanup and high-throughput LC-MS analysis of triazines in river water samples using molecularly imprinted polymers

A novel highly selective sample cleanup procedure based on the use of molecularly imprinted polymers (MIPs) as solid-phase extraction materials has been evaluated with respect to its applicability and routine use in environmental analysis. The method comprises the combination of a restricted access material (RAM) and a MIP allowing a selective sample preparation to be achieved in the online mode. This combination is called the size-selective sample separation and solvent switch (six-SPE). The RAM column combines size exclusion and adsorption chromatography, reducing the concentration of matrix molecules by a cutoff of 15 kDa. The MIP column selectively retains the triazine analytes whereas the residual matrix is not retained and separated completely. Thus, the automated RAM-MIP is capable of excluding all matrix and nontarget compounds. The cleaned and enriched extract is subsequently eluted to an HPLC column and analyzed by LC-MS. A complete on-line analysis cycle including multidimensional solid-phase extraction, separation, and detection takes less than 15 min. Terbuthylazine, atrazine, propazine, simazine, ametryn, prometryn, irgarol, and also the metabolites deethylatrazine and deisopropylatrazine can be determined without any matrix interferences, e.g., by humic acids. The whole setup is fully automated and may be continuously operated. Nonspecific interactions with the polymer are below 1% in all cases. The accuracy of the LC-MIP-LC-MS system was controlled using a certified reference material (Aquacheck). The applicability of the method to the cleanup of real samples was demonstrated by injection of contaminated river water samples. The stability of different polymers was tested by consecutive injections, and it was shown that the performance of the materials did not vary even after more than 300 enrichment and desorption cycles.

Self-assembled monolayers of rigid thiols

The preparation, structure, properties and applications of self-assembled monolayers (SAMs) of rigid 4-mercapto-biphenyls are briefly reviewed. The rigid character of the biphenyl moiety results in a molecular dipole moment that affects both the adsorption kinetics on gold surfaces, as well as the equilibrium structure of mixed SAMs. Due to repulsive intermolecular interaction, the Langmuir isotherm model does not fit the adsorption kinetics of these biphenyl thiols, and a new Ising model was developed to fit the kinetics data. The equilibrium structures of SAMs and mixed SAMs depend on the polarity of the solution from which they were assembled. Infrared spectroscopy suggests that biphenyl moieties in SAMs on gold have small tilt angles with respect to the surfaces normal. Wetting studies shows that surfaces of these SAMs are stable for months, thus providing stable model surfaces that can be engineered at the molecular level. Such molecular engineering is important for nucleation and growth studies. The morphology of glycine crystals grown on SAM surfaces depends on the structure of the nucleating glycine layer, which, in turn, depends on the H-bonding of these molecules with the SAM surface. Finally, the adhesion of PDMS cross-linked networks to SAM surfaces depends on the concentration of interfacial H-bonding. This non-linear relationship suggests that the polymeric nature of the elastomer results in a collective H-bonding effect.

CD99 (MIC2) expression in paediatric B-lineage leukaemia/lymphoma reflects maturation-associated patterns of normal B-lymphopoiesis

We have recently shown that CD99 (MIC2) is differentially expressed during normal early B-cell development in the bone marrow (BM). Since immature B-cell precursors (BCP) are assumed to correspond to some extent to acute lymphoblastic leukaemia (ALL) and non-Hodgkin's lymphoma (NHL) cells with respect to patterns of phenotypic differentiation, we wondered whether the particular maturation-associated expression patterns of CD99 in the normal BCP stages were conserved also in malignant cells. Therefore we compared malignant and physiological B cells from paediatric ALL/NHL and normal BM samples with respect to CD99 expression using selective gating and semi-quantitative flow cytometry. Common-ALLs (n = 45) were similar to their corresponding, very immature BCPs (stage 1) in expressing very high levels of CD99. Most pre-B ALLs (n = 16) were also CD99hi and thus differed from the patterns found in normal cytoplasmic mu-chain+ (cmu+) pre-B cells (stage 2, CD99lo). In particular, we found that those pre-B-ALL cases which were CD34+ also showed higher CD99 expression than the CD34- cases. This prompted us to investigate the levels of CD99 in those rare normal BCPs which also coexpress CD34 and cmu; these cells, which are transitory from stage 1 to stage 2, were found also CD99hi, thus precisely reflecting the patterns of CD34+ pre-B ALLs. The blasts of Burkitt-type B-cell ALL/NHL samples (n = 13) expressed considerably less CD99, similarly to the more differentiated BCP stages 2 (cmu+) and 3 (surface mu-chain+). In summary, we found that paediatric B-lineage malignancies display remarkable synchrony regarding the levels of CD99 expression compared to their putative normal counterparts.

Skin-associated lymphocytes in the peripheral blood of patients with atopic dermatitis: signs of subset expansion and stimulation

BACKGROUND

Skin-associated T cells are defined by the cutaneous lymphocyte-associated antigen (CLA). In atopic dermatitis (AD), CLA+ T cells harbor allergen-reactive memory cells, spontaneously secrete TH2 cytokines, and display signs of increased in vivo activation, thus relating the subset to the central disease pathomechanisms.

OBJECTIVES

It is not known whether the proportion of circulating CLA+ T cells might be expanded in AD. We were therefore prompted to compare the peripheral blood lymphocyte subpopulations of patients with AD with those of control subjects.

METHODS

We used 3-color flow cytometry to investigate age-matched peripheral blood samples of pediatric and young adult patients with mild (n = 21) or severe (n = 15) AD, patients with allergic/atopic diseases not involving the skin (n = 9), and healthy control subjects (n = 14).

RESULTS

We found no differences among the study groups with respect to the general proportions of T cells, CD4(+) T cells, CD8(+) T cells, B cells, NK cells, CD103(+) T cells, and CD25(+) T cells among total circulating lymphocytes. However, there were slightly more CD4(+) memory cells and clearly more HLA-DR+ T cells in patients with severe AD. Most remarkably, patients with severe AD had a significantly expanded proportion of CLA+ T cells (P =.024) and CLA+/CD4(+) T cells (P =.006) but similar proportions of CLA+/CD8(+) T cells compared with control subjects. Patients with severe AD also had distinctly more HLA-DR+/CLA+ T cells than control subjects (P =. 005). Similar alterations were seen in patients with mild AD, but these were not statistically significant. After correction for age, all differences were significant only in probands less than 10 years of age.

CONCLUSIONS

Circulating skin-associated T cells (CLA+) show signs of subset expansion and enhanced activation in patients with AD. These alterations, compared with control values, affect CD4(+) memory T cells in particular and are prominent only in children less than 10 years of age.

Detection of residual disease in pediatric B-cell precursor acute lymphoblastic leukemia by comparative phenotype mapping: a study of five cases controlled by genetic methods

We recently investigated samples of pediatric B-cell precursor acute lymphoblastic leukemia (BCP-ALL) and normal bone marrow (BM). We found that leukemic blasts, compared to their physiologic counterpart cells, frequently display aberrant phenotypes with respect to levels of expression of certain antigens. Using multiparameter flow cytometry, these differences enabled us to trace leukemic cells admixed to normal BM, which suggested that this approach might be a useful strategy for minimal residual disease detection. In the present study, we used the same multiparameter approach ("comparative phenotype mapping") to prove that such quantitative phenotypic differences really exist between malignant and normal BCP when simultaneously present in the BM. We demonstrate this by five exemplary follow-up BM samples from patients with BCP-ALL, all of which showed phenotypically aberrant cells according to levels of expression of CD10, CD11a, CD19, CD34, CD44, or CD45RA, as well as according to altered orthogonal light scattering properties. We confirmed the leukemic nature of these cells by polymerase chain reaction-based detection of bcr1/abl transcripts, and of leukemia clone-specific immunoglobulin heavy chain rearrangements in only the suspicious cells when sorted by flow cytometry, but not in normal BCP or non-B cells. Comparative phenotype mapping thus allows one to distinguish between normal and leukemic cells, and we show that it may enable rapid, specific, and quantitative detection of residual/resurgent leukemia in BCP-ALL.

The HTLV type I sequence from an asymptomatic German blood donor is related to sequences from South America

In most parts of Europe only a limited number of sporadic cases of HTLV-I infections have been identified. So far, the few cases found in Germany were individuals from endemic areas or with relations to endemic areas. Here we report an HTLV-I infection from an asymptomatic female German blood donor whose only known potential risk was a former partner from South America, where HTLV-I is known to be endemic. The DNA sequence of the LTR region was determined and a phylogenetic analysis indeed suggested homologies with HTLV-I sequences from South America.

Sequence analysis of the first HTLV-I infection in Germany without relations to endemic areas

In most parts of Europe only a limited number of sporadic cases of HTLV-I infections have been identified. So far, the few cases found in Germany have always been linked to individuals with relations to endemic areas. Here we report the first HTLV-I infection from a German ATL patient without any known risk for HTLV-I infection and with no relations to known endemic areas. The DNA sequence of the provirus was determined, and a phylogenetic analysis based on the LTR sequence established a close relationship with HTLV-I sequences previously found in two Romanian patients. Our data suggest the existence of a previously unrecognized cluster of HTLV-I infections in southeastern or central Europe.

Comparative phenotype mapping of normal vs. malignant pediatric B-lymphopoiesis unveils leukemia-associated aberrations

Leukemic cells of B-lineage acute lymphoblastic leukemia (ALL) are regarded as the malignant counterparts of immature, physiologic B cell precursors (BCPs). To determine whether phenotypic differences exist between these corresponding cell types, we investigated samples of normal pediatric bone marrow (n=30) as well as of B-precursor ALL at diagnosis (n=53; common and pre-B subtype). Using three-color multiparameter flow cytometric analysis, we compared the leukemic populations with the physiologic BCPs of corresponding maturity with respect to the intensity with which they expressed a series of antigens. In some of these antigens, leukemia-associated aberrations were frequently observed. In particular, overexpression of CD10 was displayed by 65% of ALL samples, whereas 58% of leukemic cases aberrantly exhibited very low or no CD45RA expression. Regarding CD11a and CD44, 47% and 35% of ALL populations were aberrant as defined by either the absence or significant overexpression of the antigen. In contrast, antigen densities of CD49d, CD49e, and CD99 on leukemic cells were in the normal range of values for BCPs. Combining the patterns of frequently aberrant markers in a comprehensive analysis, we were able to identify individual phenotypic leukemic cell aberrations in up to 98% of investigated cases. CD10 and/or CD45RA were aberrant in 86% of cases overall, emphasizing the high discriminative potential of these two markers. Using comparative phenotype mapping based on quantitatively aberrant, leukemia-associated antigenic patterns, we were able to detect leukemic blasts among normal bone marrow cells at frequencies as low as 10(-5). We speculate that our approach may have a profound impact on the development of new strategies for minimal residual disease investigations in patients with BCP-ALL.

Multiparameter phenotype mapping of normal and post-chemotherapy B lymphopoiesis in pediatric bone marrow

We studied the differentiation profiles of B cell precursors (BCP) in normal and post-chemotherapy pediatric bone marrow (BM) using multiparameter flow cytometry. The goal of our study was to draw a comprehensive phenotypic map of the three major maturational BCP stages in BM. By correlating lineage-associated markers, CD45RA, and several adhesion molecules, the stage-specific patterns were found to differ in certain details from previously published concepts. Among the earliest BCP, a subset of CD34+ CD10(lo) precursors was repeatedly observed in addition to the well characterized CD34+ CD10(hi) CD19+ majority of cells. Only two-thirds of these CD34+ CD10(lo) cells expressed CD19. However, uniformity of phenotypic features, absence of T lineage markers, and the regeneration kinetics after chemotherapy suggest the B lineage affiliation of the CD34+ CD10(lo) precursors in general. In the more mature BCP, expression of CD10, CD20, cytoplasmic and surface mu chains (c mu and s mu) was observed to overlap more than previously recognized. We found that CD20 and c mu appear early during B cell ontogeny (already on CD34+ BCP), and that CD10 is lost late, following the onset of s mu expression. Differences between normal and post-chemotherapy BM specimens regarding the phenotypic appearance of BCP were exclusively due to differences in the subset composition, as post-chemotherapy samples showed a preponderance of immature stages. Our observations may build a framework for comparing leukemic cells with their normal counterparts to define possible leukemia-associated aberrations useful for residual disease studies.

Use of a generic polymerase chain reaction assay detecting human T-lymphotropic virus (HTLV) types I, II and divergent simian strains in the evaluation of individuals with indeterminate HTLV serology

In countries with a low prevalence of human T-lymphotropic virus (HTLV) infection, indeterminate HTLV serologies are a major problem in blood bank screening because of the uncertainties about infection in these cases. The recent discovery of two new types of simian T-lymphotropic viruses (STLV), which give an HTLV-indeterminate serology, raises the question whether indeterminate serologies in humans may be linked to new types of HTLV. Starting from a Tax sequence alignment of all available primate T-cell lymphotropic virus strains (PTLV), including the two new types STLV-PH969 and STLV-PP1664, we developed generic and type-specific nested polymerase chain reactions (PCRs). The generic PCR proved to be highly sensitive and cross-reactive for all four types of PTLV, while the discriminatory PCRs had a high sensitivity and a specificity of 100%. There was no cross-reactivity with human immunodeficiency virus (HIV), ensuring correct interpretation of results from coinfected patients. Among the 77 serologically indeterminate samples tested, 6 were found to be HTLV-1 PCR positive and 1 was HTLV-II PCR positive. Sequencing of one of the HTLV-I PCR positives excluded PCR contamination, and revealed a divergent type of HTLV-I. The majority of the seroindeterminate samples (91%) were however HTLV-PCR negative, and no new types of HTLV were found. This new assay can identify otherwise undetected HTLV-I or HTLV-II infections and is a useful tool of screening for new types of HTLV among seroindeterminate samples.

Flow cytometric assessment of human MIC2 expression in bone marrow, thymus, and peripheral blood

The cell-surface expression of the MIC2 antigen defined by the monoclonal antibody 12E7 was investigated on human leukocytes in bone marrow (BM), thymus, and peripheral blood (PB) using multiparameter flow cytometry and cell sorting. In contrast to preceding reports, we found that the MIC2 antigen is not restricted to T cells and monocytes. We show that it is also expressed in the B cell and in the granulocytic lineage, the levels of expression being related to distinct maturational stages. CD34+ cells of BM were found to express the antigen at high levels. Along the granulocytic maturation pathway from CD34+CD33+ blasts to mature granulocytes, MIC2 densities appeared progressively reduced with a considerable decline at the myelocyte stage. In B lymphopoiesis, the earliest CD34+ CD10+ B-cell precursor (BCP) cells, further subdivided by expression of CD19, displayed the highest MIC2 density of BM leukocytes. All later BCP stages showed lower MIC2 expression levels, with a remarkable reduction concomitant with loss of the CD34 antigen at the CD10+CD20- surface mu-chain- stage, and a subsequent slight upregulation along with maturation to CD10-CD20high surface mu-chain+ BCPs. The brightest MIC2 expression of all cells tested was displayed by the most immature thymic T-lineage cells characterized by the antigenic profile CD34weakor- CD7++ surface CD3-CD1a(weak) CD4weak CD8-or weak. Common thymocytes stained slightly less intense with 12E7, whereas all subsequent stages of T-lineage cells in thymus, PB, or BM showed markedly reduced MIC2 levels. Mature peripheral CD4+ as well as CD8+ T cells displayed a bimodal distribution of MIC2. In the CD4+ population, the distinct MIC2 levels were related to the well-studied functional subdivision by differential expression of CD45 isoforms, the helper-inducer/memory subset showing higher MIC2 expression than helper-suppressor/naive CD4+ T cells. Similarly high MIC2 densities were found on CD16+ natural killer cells and on CD14+ monocytes, whereas mature peripheral B cells exhibited low or intermediate expression, and granulocytes exhibited no or only dim expression. These results document that the MIC2 antigen (1) is expressed on all leukocyte lineages; (2) is differentially expressed during T- and B-lymphoid, as well as granulocytic maturation; (3) shows highest expression in the most immature lymphocytic and granulocytic developmental stages; and (4) is also differentially expressed on functional T-cell subsets. We speculate that these observations imply a functional significance of MIC2 in the network of hematopoietic adhesion pathways.

[Pharmacokinetics of tetrachloroethylene in steady stage conditions]

Pharmacokinetic behaviour of tetrachloroethylene (clearance, pool, elimination kinetics, metabolic capacity) was studied by intravenous and inhalative long term administration. Concentrations of tetrachloroethylene in blood can be calculated from the concentration in the external air, as to be predicted for a substance, practically not metabolizable and eliminated totally by exhalation. The advantages of steady state techniques and their applicability to problems of industrial pharmacology are discussed.

Subunit association defects in Escherichia coli ribosome mutants lacking proteins S20 and L11

The subunit association capacity of 30S and 50S ribosomal subunits from Escherichia coli mutants lacking protein S20 or L11 as well as of 50S subunits depleted of L7/L12 was tested by sucrose gradient centrifugation and by a nitrocellulose filtration method based on the protection from hydrolysis with peptidyl-tRNA hydrolase of ribosome-bound AcPhe-tRNA. It was found that the subunits lacking either S20 or L11 display an altered association capacity, while the 50S subunits lacking L7/L12 have normal association behavior. The association of S20-lacking 30S subunits is quantitatively reduced, especially at low Mg2+ concentrations (5-12 mM), and produces loosely interacting particles which dissociate during sucrose gradient centrifugation. The association of L11-lacking 50S subunits is quantitatively near-normal at all Mg2+ concentrations and produces loosely associating particles only at low Mg2+ concentrations (5-8 mM); the mechanism of their association with 30S subunits, however, or the structure of the resulting 30S-50S couples is altered in such a way as to cause the ejection of an AcPhe-tRNA molecule pre-bound to the 30S subunits in response to poly(U).