[Palmoplantar dermatoses in children]

Dermatoses of the hands and feet cover a wide range of skin diseases that can occur in children and adolescents and are a frequent question in dermatological practice. Our synopsis of the most important differential diagnoses and their treatment is intended to provide better orientation for daily practice. A precise and detailed history is essential to establish a diagnosis, followed by clinical examination and specific examination methods. Cutaneous infection should always be excluded, as they occur very frequently. Impetigo, punctate keratolysis, blistering distal dactylitis, tinea manuum and pedum, hand-foot-mouth disease, herpes simplex digitalis and verrucae vulgaris as well as scabies are often found in the palmoplantar area and typically affect children and adolescents. In case of allergic contact dermatitis and dyshidrotic eczema, atopic diathesis in the medical history is of importance. However, we must not miss rare causes. Palmoplantar keratoses, for example, can be due to inflammatory dermatoses like pityriasis rubra pilaris (PRP) or may, as well as blistering diseases, result from hereditary disorders. Specialised centers can perform molecular genetic diagnosis and enhance patient care.

Proteasome-dependent protein quality control of the peroxisomal membrane protein Pxa1p

Peroxisomes are eukaryotic organelles that function in numerous metabolic pathways and defects in peroxisome function can cause serious developmental brain disorders such as adrenoleukodystrophy (ALD). Peroxisomal membrane proteins (PMPs) play a crucial role in regulating peroxisome function. Therefore, PMP homeostasis is vital for peroxisome function. Recently, we established that certain PMPs are degraded by the Ubiquitin Proteasome System yet little is known about how faulty/non-functional PMPs undergo quality control. Here we have investigated the degradation of Pxa1p, a fatty acid transporter in the yeast Saccharomyces cerevisiae. Pxa1p is a homologue of the human protein ALDP and mutations in ALDP result in the severe disorder ALD. By introducing two corresponding ALDP mutations into Pxa1p (Pxa1^MUT), fused to mGFP, we show that Pxa1^MUT-mGFP is rapidly degraded from peroxisomes in a proteasome-dependent manner, while wild type Pxa1-mGFP remains relatively stable. Furthermore, we identify a role for the ubiquitin ligase Ufd4p in Pxa1^MUT-mGFP degradation. Finally, we establish that inhibiting Pxa1^MUT-mGFP degradation results in a partial rescue of Pxa1p activity in cells. Together, our data demonstrate that faulty PMPs can undergo proteasome-dependent quality control. Furthermore, our observations may provide new insights into the role of ALDP degradation in ALD.

A systematic review of factors influencing treatment adherence in chronic inflammatory skin disease - strategies for optimizing treatment outcome

Adherence describes how a patient follows a medical regime recommended by a healthcare provider. Poor treatment adherence represents a complex and challenging problem of international healthcare systems, as it has a substantial impact on clinical outcomes and patient safety and constitutes an important financial burden. Since it is one of the most common causes of treatment failure, it is extremely important for physicians to reliably distinguish between non-adherence and non-response. This systematic review aims to summarize the current literature on treatment adherence in dermatology, focusing on chronic inflammatory skin diseases such as psoriasis, atopic dermatitis and acne. A systematic literature search was performed using the PubMed Database, including articles from 2008 to 2018. Low treatment adherence is a multidimensional phenomenon defined by the interplay of numerous factors and should under no circumstances be considered as the patient's fault alone. Factors influencing treatment adherence in dermatology include patient characteristics and beliefs, treatment efficacy and duration, administration routes, disease chronicity and the disease itself. Moreover, the quality of the physician-patient relationship including physician-time available for the patient plays an important role. Understanding patients' adherence patterns and the main drivers of non-adherence creates opportunities to improve adherence in the future. Strategies to increase treatment adherence range from reminder programs to simplifying prescriptions or educational interventions. Absolute adherence to treatment may not be realistically achievable, but efforts need to be made to raise awareness in order to maximize adherence as far as possible.

Refractory Anaphylaxis: Data From the European Anaphylaxis Registry

Refractory anaphylaxis (unresponsive to treatment with at least two doses of minimum 300 μg adrenaline) is a rare and often fatal hypersensitivity reaction. Comprehensive data on its definition, prevalence, and risk factors are missing. Using the data from the European Anaphylaxis Registry (11,596 cases in total) we identified refractory anaphylaxis cases (n = 42) and analyzed these in comparison to a control group of severe anaphylaxis cases (n = 4,820). The data show that drugs more frequently elicited refractory anaphylaxis (50% of cases, p < 0.0001) compared to other severe anaphylaxis cases (19.7%). Cases elicited by insects (n = 8) were more often due to bees than wasps in refractory cases (62.5 vs. 19.4%, p = 0.009). The refractory cases occurred mostly in a perioperative setting (45.2 vs. 9.05, p < 0.0001). Intramuscular adrenaline (as a first line therapy) was administered in 16.7% of refractory cases, whereas in 83.3% of cases it was applied intravenously (significantly more often than in severe anaphylaxis cases: 12.3%, p < 0.0001). Second line treatment options (e.g., vasopression with dopamine, methylene blue, glucagon) were not used at all for the treatment of refractory cases. The mortality rate in refractory anaphylaxis was significantly higher (26.2%) than in severe cases (0.353%, p < 0.0001). Refractory anaphylaxis is associated with drug-induced anaphylaxis in particular if allergens are given intravenously. Although physicians frequently use adrenaline in cases of perioperative anaphylaxis, not all patients are responding to treatment. Whether a delay in recognition of anaphylaxis is responsible for the refractory case or whether these cases are due to an overflow with mast cell activating substances—requires further studies. Reasons for the low use of second-line medication (i.e., methylene blue or dopamine) in refractory cases are unknown, but their use might improve the outcome of severe refractory anaphylaxis cases.

Interferon β-1a reduces increased interleukin-16 levels in multiple sclerosis patients

OBJECTIVES

There is convergent evidence for an important role of interleukin-16 (IL-16) in the pathogenesis of multiple sclerosis (MS). IL-16 serves as a chemoattractant for different immune cells that are involved in developing lesions. Here, we compared IL-16 levels of MS patients and controls and addressed the long-term effect of IFN-β, the most common immunomodulatory MS therapy, on IL-16 serum levels in MS patients over 2 years. Beyond this, we analysed the expression of IL-16 in two CD4(+) T-cell subsets, Th1 and Th17 cells, which are important autoimmune mediators and affected by IFN-β treatment, derived from myelin-specific T-cell transgenic mice.

MATERIALS AND METHODS

IL-16 serum levels of 17 controls and of 16 MS patients before therapy and at months 1, 2, 3, 6, 9, 12 and 24 during IFN-β1a therapy were determined by ELISA. MRI was performed before therapy, at months 12 and 24. IL-16 expression of in vitro differentiated murine myelin oligodendrocyte glycoprotein (MOG)-specific Th1 and Th17 cells was quantified by real-time PCR.

RESULTS

Before therapy, MS patients showed significantly elevated IL-16 levels compared with controls irrespective of disease activity determined by MRI. Therapy with IFN-β1a led to a significant linear decrease in IL-16 serum levels beginning after 2 months. MOG-specific Th17 cells expressed more IL-16 than Th1 cells.

CONCLUSIONS

Reduction in increased IL-16 levels may be of relevance for the therapeutic effect of IFN-β1a in MS. Easily accessible IL-16 serum levels hold a potential as biomarker of treatment efficacy in MS.

Brain volume and diffusion markers as predictors of disability and short-term disease evolution in multiple sclerosis

BACKGROUND AND PURPOSE

MRI markers of neuroaxonal damage in MS have emerged as critical long-term predictors of MS-related disability. Here we investigated the potential of whole-brain diffusivity and brain volume for the prediction of cross-sectional disability and short- to medium-term clinical evolution.

MATERIALS AND METHODS

In this multimodal prospective longitudinal MRI study of 54 patients with MS (87% under immunomodulatory therapy, baseline and follow-up at a median of 12 months), ADC histogram analysis, WM lesion load, BPF, whole-brain atrophy rate, MSFC score, and EDSS score were obtained. A total of 44 patients with no relapse at both time points were included.

RESULTS

At both time points, ADC histogram analysis provided robust predictors of the MSFC scores (maximal R(2) = 0.576, P < .001), incorporated cognition and fine-motor skill subscores, and EDSS scores. Significant changes beyond physiologic age-related changes at follow-up were noted for ADC histogram markers and BPF. Stronger diffusivity alterations and brain volume at baseline predicted MSFC decline, as demonstrated by multiple linear regression analysis (mean ADC, R(2) = 0.203; P = .003) and lower baseline BPF in patients with declined compared with stable MSFC scores (P = .001). Results were independent of intercurrent relapses.

CONCLUSIONS

Diffusion histogram analysis provided stable surrogates of disability in MS and proved sensitive for monitoring disease progression during a median of 12 months. Advanced neuroaxonal pathology at baseline was indicative of an increased risk for sustained progression during a median of 12 months, independent of intercurrent relapses.

More CLEC16A gene variants associated with multiple sclerosis

OBJECTIVES

Recently, associations of several single-nucleotide polymorphisms (SNPs) within the CLEC16A gene with multiple sclerosis (MS), type-I diabetes, and primary adrenal insufficiency were reported.

METHODS

We performed linkage disequilibrium (LD) fine mapping with 31 SNPs from this gene, searching for the region of highest association with MS in a German sample consisting of 603 patients and 825 controls.

RESULTS

Four SNPs located in intron 19 of the CLEC16A gene were found associated. We could replicate the finding for SNP rs725613 and were able to show for the first time the association of rs2041670, rs2080272 and rs998592 with MS.

CONCLUSION

All described base polymorphisms are mapping to one LD block of approximately 50 kb within intron 19 of the CLEC16A gene, suggesting a pivotal role of this region for susceptibility of MS and possibly also for other autoimmune diseases.

Improved version of the red fluorescent protein (drFP583/DsRed/RFP)

GFP has established itself as a highly useful tool throughout many areas of modern biology. Recently, the novel fluorescent protein drFP583, also termed DsRed or RFP, was clonedfrom a coral of the Discosoma genus. The protein is only weakly homologous to GFP and has a red emission spectrum, which makes drFP583 an attractive candidate for in vivo double labeling together with GFP variants. However, wildtype drFP583 has several drawbacks, including inefficient folding of the protein, extremely slow maturation of the chromophore, and tetramerization even in dilute solutions. Here we report on important improvements to this reporter that lead to higher levels of fluorescent drFP583 species in the cell. We further characterized our best mutant for applications in yeast and mammalian cell biology.

Glycoside carbamates from benzoxazolin-2(3H)-one detoxification in extracts and exudates of corn roots

Zea mays was incubated with the natural phytotoxin benzoxazolin-2(3H)-one (BOA) to investigate the detoxification process. A hitherto unknown detoxification product, 1-(2-hydroxyphenylamino)-1-deoxy-beta-gentiobioside 1,2-carbamate (3), was isolated and identified. A reinvestigation of known BOA detoxification products by NMR methods led to the finding that the structure of benzoxazolin-2(3H)-one-N-beta-glucoside (1) first reported from Avena sativa has to be revised. In fact, the correct structure is that of the isomeric 1-(2-hydroxyphenylamino)-1-deoxy-beta-glucoside 1,2-carbamate 2, which is structurally related to 3. It was now shown with a synthetic mixture of 1 and 2 that 1 underwent spontaneous isomerization to form 2 in solution. Thus, N-glucosylation of BOA in the plant led finally to the carbamate 2. In contrast to BOA-6-O-glucosylation, BOA-induced N-glucosylation appears first after 6-8 h of incubation. As soon as N-glucosylation is possible, BOA-6-O-glucoside is not further accumulated, whereas the amount of glucoside carbamate increases continuously during the next 40 h. Synthesis of gentiobioside carbamate seems to be a late event in BOA detoxification. All detoxification products are released into the environment via root exudation.

A screen for genes required for meiosis and spore formation based on whole-genome expression

BACKGROUND

Meiosis is the process by which gametes are generated with half the ploidy of somatic cells. This reduction is achieved by three major differences in chromosome behavior during meiosis as compared to mitosis: the production of chiasmata by recombination, the protection of centromere-proximal sister chromatid cohesion, and the monoorientation of sister kinetochores during meiosis I. Mistakes in any of these processes lead to chromosome missegregation.

RESULTS

To identify genes involved in meiotic chromosome behavior in Saccharomyces cerevisiae, we deleted 301 open reading frames (ORFs) which are preferentially expressed in meiotic cells according to microarray gene expression data. To facilitate the detection of chromosome missegregation mutants, chromosome V of the parental strain was marked by GFP. Thirty-three ORFs were required for the formation of wild-type asci, eight of which were needed for proper chromosome segregation. One of these (MAM1) is essential for the monoorientation of sister kinetochores during meiosis I. Two genes (MND1 and MND2) are implicated in the recombination process and another two (SMA1 and SMA2) in prospore membrane formation.

CONCLUSIONS

Reverse genetics using gene expression data is an effective method for identifying new genes involved in specific cellular processes.

Role of the spindle pole body of yeast in mediating assembly of the prospore membrane during meiosis

Spindle pole bodies (SPBs) are the centrosome equivalents in yeast, required for microtubule organization. In yeast, the SPB further serves as the attachment sites of the prospore membrane during meiosis. Here we report the identification of two new meiosis-specific components of the SPB, Mpc54p and Mpc70p, and the first protein specific for the prospore membrane, Don1p. Mpc54p and Mpc70p are not present in mitotic SPBs, and during meiosis II they are components of a meiosis-specific structural alteration of the outer plaque of the SPB. Both proteins are dispensable for the meiotic divisions but are essentially required for the formation of the prospore membrane. In the mpc54 and mpc70 mutants, the Don1p-containing precursors of the prospore membrane can still be found in the cytoplasm and associated with the SPB. Unexpectedly, however, the assembly of the precursors to a continuous membrane system is affected. Thus, the meiotic SPB is directly involved in the formation of a specialized membrane system, the membrane of the prospore.

Interaction of the yeast gamma-tubulin complex-binding protein Spc72p with Kar1p is essential for microtubule function during karyogamy

The spindle pole body component Kar1p has a function in nuclear fusion during conjugation, a process known as karyogamy. The molecular role of Kar1p during this process is poorly understood. Here we show that the yeast gamma-tubulin complex-binding protein Spc72p interacts directly with the N-terminal domain of Kar1p, thereby targeting the gamma-tubulin complex to the half bridge, a substructure of the spindle pole body, where it organizes microtubules. This binding of Spc72p to Kar1p has only a minor role during vegetative growth, whereas it becomes essential for karyogamy in mating cells, explaining the important role of Kar1p in this process. We also show that the localization of Spc72p within the spindle pole body changes throughout the cell cycle and even more strongly in response to mating pheromone. Taken together, these observations suggest that the relocalization of Spc72p within the spindle pole body is the 'landmark' event in the pheromone-induced reorganization of the cytoplasmic microtubules.

Epitope tagging of yeast genes using a PCR-based strategy: more tags and improved practical routines

Epitope tagging of proteins as a strategy for the analysis of function, interactions and the subcellular distribution of proteins has become widely used. In the yeast Saccharomyces cerevisiae, molecular biological techniques have been developed that use a simple PCR-based strategy to introduce epitope tags to chromosomal loci (Wach et al., 1994). To further employ the power of this strategy, a variety of novel tags was constructed. These tags were combined with different selectable marker genes, resulting in PCR amplificable modules. Only one set of primers is required for the amplification of any module. Furthermore, convenient laboratory techniques are described that facilitate the genetic manipulations of yeast strains, as well as the analysis of the epitope-tagged proteins.

Spc29p is a component of the Spc110p subcomplex and is essential for spindle pole body duplication

In yeast, microtubules are organized by the spindle pole body (SPB). The SPB is a disk-like multilayered structure that is embedded in the nuclear envelope via its central plaque, whereas the outer and inner plaques are exposed to the cytoplasm and nucleoplasm, respectively. How the SPB assembles is poorly understood. We show that the inner/central plaque is composed of a stable SPB subcomplex, containing the gamma-tubulin complex-binding protein Spc110p, calmodulin, Spc42p, and Spc29p. Spc29p acts as a linker between the central plaque component Spc42p and the inner plaque protein Spc110p. Evidence is provided that the calmodulin-binding site of Spc110p influences the binding of Spc29p to Spc110p. Spc42p also was identified as a component of a cytoplasmic SPB subcomplex containing Spc94p/Nud1p, Cnm67p, and Spc42p. Spc29p and Spc42p may be part of a critical interface of nucleoplasmic and cytoplasmic assembled SPB subcomplexes that form during SPB duplication. In agreement with this, overexpressed Spc29p was found to be a nuclear protein, whereas Spc42p is cytoplasmic. In addition, an essential function of SPC29 during SPB assembly is indicated by the SPB duplication defect of conditional lethal spc29(ts) cells and by the genetic interaction of SPC29 with CDC31 and KAR1, two genes that are involved in SPB duplication.

Microtubule organization by the budding yeast spindle pole body

In budding yeast microtubule organizing functions are provided by the spindle pole body (SPB), a multi-layered structure that is embedded in the nuclear envelope throughout the cell cycle. The SPB organizes the nuclear and cytoplasmic microtubules which are spatially and functionally distinct. Microtubule formation in yeast requires the Tub4p-complex, containing the gamma-tubulin Tub4p, and two additional proteins, the SPB components Spc97p and Spc98p. The Tub4p complex assembles in the cytoplasm and is then anchored to the sides of the SPB which organize microtubules. This is achieved by the binding of Spc97p and Spc98p to so-called gamma-tubulin complex binding proteins (GTBPs) at the SPB. Spc72p is the yeast GTBP at the cytoplasmic side of the SPB, while Spc110p is the nuclear GTBP. Both GTBPs control the number of Tub4p complexes associated with the SPB and thereby the number of microtubules formed. In addition, the GTBPs may regulate the activity of the Tub4p complex. Homologues of Spc97p and Spc98p have been identified from yeast to mammalian cells and these are also part of gamma-tubulin complexes, suggesting that these related proteins may also interact with GTBPs at the centrosome. Candidates for GTBPs have been identified in mammalian and insect cells.

Receptors determine the cellular localization of a gamma-tubulin complex and thereby the site of microtubule formation

The yeast microtubule organizing centre (MTOC), known as the spindle pole body (SPB), organizes the nuclear and cytoplasmic microtubules which are functionally and spatially distinct. Microtubule organization requires the yeast gamma-tubulin complex (Tub4p complex) which binds to the nuclear side of the SPB at the N-terminal domain of Spc110p. Here, we describe the identification of the essential SPB component Spc72p whose N-terminal domain interacts with the Tub4p complex on the cytoplasmic side of the SPB. We further report that this Tub4p complex-binding domain of Spc72p is essential and that temperature-sensitive alleles of SPC72 or overexpression of a binding domain-deleted variant of SPC72 (DeltaN-SPC72) impair cytoplasmic microtubule formation. Consequently, polynucleated and anucleated cells accumulated in these cultures. In contrast, overexpression of the entire SPC72 results in more cytoplasmic microtubules compared with wild-type. Finally, exchange of the Tub4p complex-binding domains of Spc110p and Spc72p established that the Spc110p domain, when attached to DeltaN-Spc72p, was functional at the cytoplasmic site of the SPB, while the corresponding domain of Spc72p fused to DeltaN-Spc110p led to a dominant-negative effect. These results suggest that different components of MTOCs act as receptors for gamma-tubulin complexes and that they are essential for the function of MTOCs.

Spc98p directs the yeast gamma-tubulin complex into the nucleus and is subject to cell cycle-dependent phosphorylation on the nuclear side of the spindle pole body

In the yeast Saccharomyces cerevisiae, microtubules are organized by the spindle pole body (SPB), which is embedded in the nuclear envelope. Microtubule organization requires the gamma-tubulin complex containing the gamma-tubulin Tub4p, Spc98p, and Spc97p. The Tub4p complex is associated with cytoplasmic and nuclear substructures of the SPB, which organize the cytoplasmic and nuclear microtubules. Here we present evidence that the Tub4p complex assembles in the cytoplasm and then either binds to the cytoplasmic side of the SPB or is imported into the nucleus followed by binding to the nuclear side of the SPB. Nuclear import of the Tub4p complex is mediated by the essential nuclear localization sequence of Spc98p. Our studies also indicate that Spc98p in the Tub4p complex is phosphorylated at the nuclear, but not at the cytoplasmic, side of the SPB. This phosphorylation is cell cycle dependent and occurs after SPB duplication and nucleation of microtubules by the new SPB and therefore may have a role in mitotic spindle function. In addition, activation of the mitotic checkpoint stimulates Spc98p phosphorylation. The kinase Mps1p, which functions in SPB duplication and mitotic checkpoint control, seems to be involved in Spc98p phosphorylation. Our results also suggest that the nuclear and cytoplasmic Tub4p complexes are regulated differently.

Spc98p and Spc97p of the yeast gamma-tubulin complex mediate binding to the spindle pole body via their interaction with Spc110p

Previously, we have shown that the yeast gamma-tubulin, Tub4p, forms a 6S complex with the spindle pole body components Spc98p and Spc97p. In this paper we report the purification of the Tub4p complex. It contained one molecule of Spc98p and Spc97p, and two or more molecules of Tub4p, but no other protein. We addressed how the Tub4p complex binds to the yeast microtubule organizing center, the spindle pole body (SPB). Genetic and biochemical data indicate that Spc98p and Spc97p of the Tub4p complex bind to the N-terminal domain of the SPB component Spc110p. Finally, we isolated a complex containing Spc110p, Spc42p, calmodulin and a 35 kDa protein, suggesting that these four proteins interact in the SPB. We discuss in a model, how the N-terminus of Spc110p anchors the Tub4p complex to the SPB and how Spc110p itself is embedded in the SPB.

The spindle pole body component Spc97p interacts with the gamma-tubulin of Saccharomyces cerevisiae and functions in microtubule organization and spindle pole body duplication

Previously, we have shown that the gamma-tubulin Tub4p and the spindle pole body component Spc98p are involved in microtubule organization by the yeast microtubule organizing centre, the spindle pole body (SPB). In this paper we report the identification of SPC97 encoding an essential SPB component that is in association with the SPB substructures that organize the cytoplasmic and nuclear microtubules. Evidence is provided for a physical and functional interaction between Tub4p, Spc98p and Spc97p: first, temperature-sensitive spc97(ts) mutants are suppressed by high gene dosage of SPC98 or TUB4. Second, Spc97p interacts with Spc98p and Tub4p in the two-hybrid system. Finally, immunoprecipitation and fractionation studies revealed complexes containing Tub4p, Spc98p and Spc97p. Further support for a direct interaction of Tub4p, Spc98p and Spc97p comes from the toxicity of strong SPC97 overexpression which is suppressed by co-overexpression of TUB4 or SPC98. Analysis of temperature-sensitive spc97(ts) alleles revealed multiple spindle defects. While spc97-14 cells are either impaired in SPB separation or mitotic spindle formation, spc97-20 cells show an additional defect in SPB duplication. We discuss a model in which the Tub4p-Spc98p-Spc97p complex is part of the microtubule attachment site at the SPB.

[Sanitation of biowaste compost by using Salmonella enteritidis as a pathogen indicator and survival of Salmonella in seepage water]

The following investigations show the frequency of the occurrence of Salmonella in biowastes. Salmonellae, belonging to the serotypes Salmonella enteritidis, infantis and agona were detected in 50% of the investigated biowaste samples. In order to control the reliability of compositing techniques on eliminating pathogens, Salmonella enteritidis was used as a pathogen indicator, which was brought into a container composting process and investigated on it's decline. Although the input indicator bacteria were eliminated in every case latest until the end of container composting, Salmonella was detected in 36% of the investigated fresh compost samples. Every time when Salmonella was detected in input material, the same serotypes were to be found in seepage water and survived there until the end of intensive rot. In laboratory experiments the maximum survival time of Salmonella enteritidis in seepage water at +5 degrees C was 42 days. Seepage water was found out to be a reservoir for survival of Salmonellae and has to be considered as a permanent source of contamination. In the question of the disposal of seepage water there are disagreements between the instructions of TA Siedlungsabfall and TA Luft.

N-Glycosylation affects endoplasmic reticulum degradation of a mutated derivative of carboxypeptidase yscY in yeast

The endoplasmic reticulum (ER) of eukaryotic cells contains a quality control system, that is required for the proteolytic removal of aberrantly folded proteins that accumulate in this organelle. We used genetic and biochemical methods to analyse the involvement of N-glycosylation in the degradation of a mutant derivative of carboxypeptidase yscY in the ER of the yeast Saccharomyces cerevisiae. Our results demonstrate that N-glycosylation of this protein is required for its degradation since an unglycosylated species is retained stably in the ER. Cells that were devoid of the ER-processing alpha 1,2-mannosidase showed reduced degradation of the glycosylated substrate protein. Disruption of CNE1, a gene encoding a putative yeast homologue for calnexin, did not exhibit any effects on the degradation of this substrate protein in vivo. Also, the alpha 1,2-mannosidase-dependent reduction in the degradation rate did not show any correlation with the function of the CNE1 gene product. Our results suggest that the ER of yeast contains a glycosylation-dependent quality control system, as has been shown for higher eukaryotic cells.

The spindle pole body component Spc98p interacts with the gamma-tubulin-like Tub4p of Saccharomyces cerevisiae at the sites of microtubule attachment

Tub4p is a novel tubulin found in Saccharomyces cerevisiae. It most resembles gamma-tubulin and, like it, is localized to the yeast microtubule organizing centre, the spindle pole body (SPB). In this paper we report the identification of SPC98 as a dosage-dependent suppressor of the conditional lethal tub4-1 allele. SPC98 encodes an SPB component of 98 kDa which is identical to the previously described 90 kDa SPB protein. Strong overexpression of SPC98 is toxic, causing cells to arrest with a large bud, defective microtubule structures, undivided nucleus and replicated DNA. The toxicity of SPC98 overexpression was relieved by co-overexpression of TUB4. Further evidence for an interaction between Tub4p and Spc98p came from the synthetic toxicity of tub4-1 and spc98-1 alleles, the dosage-dependent suppression of spc98-4 by TUB4, the binding of Tub4p to Spc98p in the two-hybrid system and the co-immunoprecipitation of Tub4p and Spc98p. In addition, Spc98-1p is defective in its interaction with Tub4p in the two-hybrid system. We suggest a model in which Tub4p and Spc98p form a complex involved in microtubule organization by the SPB.

Der1, a novel protein specifically required for endoplasmic reticulum degradation in yeast

The endoplasmic reticulum (ER) of the yeast Saccharomyces cerevisiae contains of proteolytic system able to selectively degrade misfolded lumenal secretory proteins. For examination of the components involved in this degradation process, mutants were isolated. They could be divided into four complementation groups. The mutations led to stabilization of two different substrates for this process. The mutant classes were called 'der' for 'degradation in the ER'. DER1 was cloned by complementation of the der1-2 mutation. The DER1 gene codes for a novel, hydrophobic protein, that is localized to the ER. Deletion of DER1 abolished degradation of the substrate proteins. The function of the Der1 protein seems to be specifically required for the degradation process associated with the ER. The depletion of Der1 from cells causes neither detectable growth phenotypes nor a general accumulation of unfolded proteins in the ER. In DER1-deleted cells, a substrate protein for ER degradation is retained in the ER by the same mechanism which also retains lumenal ER residents. This suggests that DER1 acts in a process that directly removes protein from the folding environment of the ER.

Vacuolar/lysosomal proteolysis: proteases, substrates, mechanisms

Proteolysis is an essential post-transcriptional process. The lysosome/vacuole is the central organelle for non-specific proteolysis in eukaryotes. Most proteases that work in the lysosome enter it via the secretory pathway. The bulk of proteins to be degraded enter this proteolytic compartment via endocytosis and autophagocytosis. Our understanding of the mechanisms involved in these processes has increased considerably, and the information obtained in these studies has enabled new, specific proteolytic pathways to be investigated in other cellular compartments, particularly in the cytoplasm.

Analysis of two mutated vacuolar proteins reveals a degradation pathway in the endoplasmic reticulum or a related compartment of yeast

The fate of a mutant form of each of the two yeast vacuolar enzymes proteinase yscA (PrA) and carboxypeptidase yscY (CPY) has been investigated. Both mutant proteins are rapidly degraded after entering the secretory pathway. Mutant PrA is deleted in 37 amino acids spanning the processing site region of the PrA pro-peptide. The mutant enzyme shows no activity towards maturation of itself or other vacuolar hydrolases, a function of wild-type PrA. Mutant CPY carries an Arg instead of a Gly residue in a highly conserved region, two positions distant from the active-site Ser. In contrast to wild-type CPY, the mutant form was quickly degraded by trypsin in vitro, indicating an altered structure. Using antisera specific for alpha-1-->6 and alpha-1-->3 outer-chain mannose linkages, no Golgi-specific carbohydrate modification could be detected on either mutant protein. Subcellular fractionation studies located both mutant enzymes in the endoplasmic reticulum. Degradation kinetics of both proteins show the same characteristics, indicating similar degradation pathways. The degradation process was shown to be independent of a functional sec18 gene product and takes place before Golgi-specific carbohydrate modifications occur. The proteasome, the major proteolytic activity of the cytoplasm, is not involved in this degradation event. All degradation characteristics of the two mutant proteins are consistent with a degradation process within the endoplasmic reticulum ('ER degradation').

Autophagy in frog visual cells in vitro

Isolated frog retinas were incubated in a medium free of serum and amino acids under dim white incandescent light of 20 lux/m2. After 1, 2, 6, and 9 hr of incubation, six retinas at each time point were fixed for electron microscopic investigation. Histochemical staining of acid phosphatase was performed in control and experimental tissues. Autophagic vacuoles in visual cell inner segments were counted and compared with the incidence of vacuoles in control tissues. The ratio of newly formed: old autophagic vacuoles was assessed in incubated retinas, and the number of autophagic vacuoles per rod cell and per cone cell was evaluated. The results indicated that the number of autophagic vacuoles was significantly increased from 1 to 9 hr of incubation, the ratio of newly formed: old autophagic vacuoles was constant over this period, and the amount of autophagy occurring in rods and cones was similar. In a second group of experiments, retinas were incubated under the same conditions but at two different levels of illumination. One series of retinas was incubated in dim red incandescent light of 5 lux/m2, the other series was incubated at bright white fluorescent light of 300 lux/m2. The total numbers of autophagic vacuoles showed a consistent elevation of 20% in bright white light material as compared wot dim red light material. Autophagic vacuoles per cone were significantly higher in retinas incubated in white light than in retinas incubated in red light. Autophagic vacuoles per rod were about equal in both groups. Our observations indicated that visual cells contain an intracellular mechanism of degradation, which is increased under changed metabolic conditions and modified as a function of different levels of illumination.