A 140-base-pair repetitive sequence element in the mouse rRNA gene spacer enhances transcription by RNA polymerase I in a cell-free system

We show that the repetitive 140-base-pair (bp) elements present in the spacer of mouse rRNA genes function as enhancers for RNA polymerase I. Attachment of these elements to the rDNA promoter stimulates rRNA synthesis both in vivo and in vitro. The cis-activating effect of the spacer repeats is orientation-independent and increases with increasing numbers of the 140-bp elements. Competition experiments demonstrate that the spacer repeats bind one or more of the transcription factors interaction with the rDNA promoter. Both the 140-bp elements and the core promoter act cooperatively and thus are functionally linked. The 60/81-bp enhancer repeats from Xenopus laevis rDNA compete for a murine transcription factor(s) and stimulate transcription often fused to the mouse rDNA promoter. The results indicate that despite the marked species specificity of rDNA transcription initiation, common factors may interact with both the rDNA promoter and the enhancer.

Initial steps in protein membrane insertion. Bacteriophage M13 procoat protein binds to the membrane surface by electrostatic interaction

Bacteriophage M13 procoat protein is synthesized on free polysomes prior to its assembly into the inner membrane of Escherichia coli. As an initial step of the membrane insertion pathway, the precursor protein interacts with the cytoplasmic face of the inner membrane. We have used oligonucleotide-directed mutagenesis to study the regions of the procoat protein involved in membrane binding. We find that there is an absolute requirement for positively charged amino acids at both ends of the protein. Replacing these with negatively charged residues resulted in an accumulation of the precursor in the cytoplasm. We propose that the positively charged amino acids are directly involved in membrane binding, possibly directly to the negatively charged phospholipid head groups. This was tested in vitro with artificial liposomes. Whereas wild-type procoat interacted with these liposomes, we found that procoat mutants with negatively charged amino acids at both ends did not bind. Therefore, we conclude that newly synthesized M13 procoat protein binds electrostatically to the negatively charged inner membrane of E. coli.

Efficient translocation of positively charged residues of M13 procoat protein across the membrane excludes electrophoresis as the primary force for membrane insertion

The coat protein of bacteriophage M13 is inserted into the Escherichia coli plasma membrane as a precursor protein, termed procoat, with a typical leader peptide of 23 amino acid residues. Its membrane insertion requires the electrochemical potential but not the cellular components SecA and SecY. Since the electrochemical gradients result in the periplasmic side of the membrane being positively charged, the membrane potential could contribute to the transfer of the negatively charged central region of procoat across the membrane. Here we demonstrate that the central domain following the leader peptide can be translocated across the membrane even when the net charge of the region is changed from -3 to +3. This rules out an electrophoresis-like insertion mechanism for procoat. We also show that the sec independence of procoat insertion is linked to the presence of the second apolar domain. The deletion of most of the second apolar domain from a procoat fusion protein results in sec dependent membrane insertion of the hybrid protein. Moreover, like other proteins that require the sec genes, translocation of this sec dependent procoat protein is inhibited when positively charged residues are introduced after the leader peptide. Loop models involving one or two hydrophobic regions are presented that account for the differences in tolerance of positively charged residues.

Strobilurins F, G and H, three new antifungal metabolites from Bolinea lutea. I. Fermentation, isolation and biological activity

Three new strobilurins F, G and H, antibiotics with antifungal activity, were isolated from cultures of Bolinea lutea Sacc. These new compounds differ from previously described analogs in their aromatic substitution. An HPLC method allows complete separation of all the components.

Specific interaction of the murine transcription termination factor TTF I with class-I RNA polymerases

The 18-base-pair sequence element AGGTCGACCAGTACTCCG (the Sal box) signals termination of mouse ribosomal gene transcription. This sequence is recognized by a sequence-specific DNA-binding protein, TTF I, which mediates the termination of transcription by RNA polymerase I (pol I). Subsequently, the ends of the primary transcripts are trimmed by 10 nucleotides in a sequence-dependent 3'-terminal processing reaction. We have now investigated whether TTF I bound to its target sequence will block elongation by any RNA polymerase by steric hindrance, or whether it is specific for elongation by pol I. The results demonstrate that TTF I directs transcription termination with RNA polymerase I from species as divergent as mouse and yeast, but fails to affect elongation by heterologous polymerases (eukaryotic RNA polymerases II and III, Escherichia coli or bacteriophage T3 RNA polymerase). By contrast, purified lac repressor bound to its operator sequence stops elongation by both RNA polymerase I and II.

[Lymphomatoid papulosis resembling ecthyma. A case report]

A 54-year-old female patient recurrently developed disseminated papules, red-brown in color and partly ulcerous, which spontaneously disappeared after 3-6 weeks. Histological examination revealed dense infiltration of atypical lymphocytes with epidermotropism. Immunohistological analysis showed predominantly helper T-cells (CD 4). Accordingly, we established the diagnosis of lymphomatoid papulosis. There was no evidence of malignant lymphoma.

Immunostaining of keratin and vimentin in epidermis: comparison of different post-embedding immunogold techniques for electron microscopy

The present study compares different post-embedding staining methods, including conventional and low-temperature embedding techniques, for demonstration of the keratin and vimentin cytoskeleton of epidermal cells, applying commercially available polyclonal and monoclonal antibodies. Immunogold staining (5-nm particles) was performed on the following material: (a) osmium-fixed and Durcupan-embedded material, etched with various solutions; (b) aldehyde-fixed material embedded in Lowicryl K4M at 4 degrees C and -35 degrees C; (c) aldehyde-fixed material embedded in Lowicryl K11M at -60 degrees C with and without cryoprotection with glycerol. In conventionally embedded material we failed to demonstrate intermediate filaments, whereas they were stained after low-temperature embedding with Lowicryl, i.e., K4M 4 degrees C, K4M -35 degrees C, and K11M -60 degrees C. The keratin and vimentin cytoskeleton reacted exclusively with polyclonal antibodies. The best results for antigenicity as well as structural preservation were achieved by post-embedding staining of K4M -35 degrees C-embedded material. Antibodies to keratin stained the cytoskeleton in keratinocytes of all epidermal layers. Filaments were decorated in a linear alignment. Antibodies to vimentin stained the cytoskeleton of Langerhans cells and melanocytes. In these cells a linear distribution pattern of the reaction product along the filaments and an extrafilamentous cluster formation were observed, indicating staining of vimentin and a vimentin-associated protein.

3'-end formation of mouse pre-rRNA involves both transcription termination and a specific processing reaction

We have studied the sequence requirements for 3'-end formation of rDNA transcripts in a cell-free system and show that the generation of correct ends of mouse pre-rRNA is brought about by a two-step process that involves a bona fide termination reaction, followed by a specific trimming of the primary transcript by 10 nucleotides. We show that termination of mouse ribosomal gene transcription by RNA polymerase I (pol I) takes place in front of an 18-bp DNA sequence element (the 'Sal box'), which was previously shown to function as termination signal. Termination of pol I transcription occurs at a fixed distance (11 bp) upstream of the Sal box, independent of the sequence of adjacent gene regions. The processing reaction, however, is strongly influenced by sequences flanking the termination signal at the 5' site. Substitution of a cluster of T residues by guanines within the region of 3'-end formation abolishes the 3'-terminal trimming of the primary transcript. Interestingly, this 3'-terminal processing event, which can be uncoupled from the termination reaction, requires both a correct 3' end and specific sequences in the 3'-terminal region of the primary transcript. Read-through transcripts generated in the extract system or by SP6 RNA polymerase are no substrate for the processing nuclease(s). Because the termination and processing activity can be separated chromatographically, the nucleolytic activity does not reside in TTF-I, the factor that binds to the Sal box and directs transcription termination.

Alterations in the extracellular domain of M13 procoat protein make its membrane insertion dependent on secA and secY

The products of genes secA and secY (SecA and SecY) are putative components of a bacterial protein export machinery and are required for the export of many periplasmic and membrane proteins. Only a few proteins, among them the M13 procoat protein, insert independently of SecA and SecY. To investigate the reason why the procoat protein inserts independently of sec functions, various hybrid proteins were constructed. By in-frame gene fusions the central procoat region, which translocates across the membrane, was extended in size. Fragments of the ompA gene ranging from 522-294 bp were ligated with the procoat gene. The hybrid proteins were inserted into the membrane and processed normally, but only in the presence of functional SecA and SecY.

Malignant blue nevus with metastases to the lung

A malignant blue nevus of the right upper arm with hematogeneous lung metastases is presented. Histological examination showed that the tumor was composed of spindle, dendritic, and globular cells with hyperchromatic and polymorphic nuclei, atypical mitoses, and tumor cell necrosis. There was no proliferation of atypical melanocytes at the dermoepidermal junction. Histologically, malignant blue nevus should be distinguished from benign cellular blue nevus, primary cutaneous malignant melanoma, cutaneous metastases of malignant melanoma, and clear cell sarcoma.

[Vesicular pityriasis rosea]

Pityriasis rosea is a frequently occurring skin disease of unknown aetiology. Ten clinical forms of this disease are known, with predominance of the macular type. We observed a healthy 24-year-old patient with the very rare vesicular variant of pityriasis rosea, which has to be differentiated from vesicular virus and drug-induced eruptions.

[Vater-Pacini neurofibroma]

We report on a 49-year-old female patient suffering from Pacinian neurofibroma on her right middle finger. The microscopical findings of this rare neoplasm are discussed in detail.

[Elastofibroma dorsi]

We report on an 80-years-old woman suffering from subacute prurigo simplex, who had developed a painless subcutaneous tumor on her right upper back, 8 cm in diameter. In palpation, the tumor was firm and did not adhere to the overlying skin. The movability of her arms and back was not restricted. The tumor could not be distinguished from its surrounding tissue by means of ultrasound. Surgery revealed that the tumor was firmly attached to the thoracic fasciae, periosteum, and ligaments, which prevented its complete removal. On histological examination, the tumor was diagnosed as elastofibroma dorsi. We discuss our microscopical findings of this very rare neoplasm in detail.

[Immunohistological studies of immune dermatoses on reconstituted paraffin sections. Value and comparison of different methods]

In a study on 26 patients with autoimmune diseases the immunostaining for immunoglobulins and complement in frozen sections was compared with that in formalin-fixed and paraffin-embedded sections. The formalin-fixed material of pemphigus vulgaris, lupus erythematosus, bullous pemphigoid, and dermatitis herpetiformis (Duhring's disease) was reconstituted and stained by means of the standard two-step technique (TST), the peroxidase-antiperoxidase technique (PAP), and the streptavidin-biotin method (SAB). In comparison with frozen sections, immunoglobulins and complement could also be demonstrated in formalin-fixed sections in all cases of pemphigus vulgaris and in 85% of cases of discoid lupus erythematosus, but in only 60% of cases of bullous pemphigoid or Duhring's disease. PAP and SAB proved to be about equally reliable, but TST was significantly less dependable.

The mouse ribosomal gene terminator consists of three functionally separable sequence elements

The structural requirements for 3' end formation of mouse pre-rRNA have been studied. Three sequence elements are shown to be required for accurate and efficient transcription termination by RNA polymerase I (pol I) assayed both in a cell-free transcription system and in vivo after transfection of rDNA minigene constructs into 3T6 cells. The essential termination signal is the previously identified 18-bp conserved element (AGGTCGACCAGATTANTCCG) that contains a SalI restriction site. This sequence motif (the 'Sal box') interacts with a specific nuclear protein that directs transcription termination. Here we demonstrate that the 'Sal box' sequence motif is sufficient for termination of pol I transcripts and the release of the nascent RNA chains from the template. However, in addition to this termination signal, pyrimidine-rich sequences flanking the box at the 5' and 3' side play a role in the efficient and correct formation of authentic pre-rRNA termini. Downstream sequences contribute to the efficiency of the termination reaction, whereas the position of 3' end formation (i.e. 21 bp upstream of the 'Sal box') is affected by 5' flanking regions. These flanking regions are recognized by at least two different nuclear factors which specifically bind to DNA sequences located upstream and downstream of the 'Sal box'.

Bacteriophage M13 procoat protein inserts into the plasma membrane as a loop structure

The major coat protein of bacteriophage M13 is synthesized as a precursor, the procoat, with a typical leader (signal) sequence of 23 residues at its NH2-terminus. A fusion protein that contains the NH2-terminal 141 residues of cytoplasmic ribulokinase and all but the first ten residues of M13 procoat was made. The fusion protein inserts into the plasma membrane of Escherichia coli and is processed by leader peptidase to give rise to a leader peptide of 155 residues and the mature coat protein of 50 residues. The NH2-terminus of the leader peptide remains in the cytoplasm and is protected from protease added to the medium outside of the cell. This indicates that M13 procoat inserts into the membrane as a loop structure and that the NH2-terminus of a leader peptide remains within the cytoplasm during membrane insertion.

A novel promoter in the mouse rDNA spacer is active in vivo and in vitro

We have identified a novel RNA polymerase I (pol I) transcription initiation site within the 'non-transcribed' spacer of mouse rDNA. This spacer promoter is located about 2 kb upstream of the 45S pre-rRNA promoter and directs specific transcription initiations both in a cell-free system using truncated templates and in vivo after transfection into mouse cells. The spacer promoter contains an 11 out of 16 bases match to the core element of the major ribosomal gene promoter and is oriented in the same direction. It exerts a significantly lower transcriptional activity as compared to the 45S pre-rRNA promoter. The elongation of transcripts initiated at the spacer promoter is stopped at a termination signal located 170 bp upstream of the pre-rRNA start site. Since it has been previously shown that, in addition to its terminator function, the same sequence motif acts as an upstream element of the adjacent gene promoter, the function of the spacer promoter may be to capture free pol I molecules and drive them to the gene promoter in order to achieve the high level of transcription characteristic of eukaryotic rRNA genes.

The internal signal sequence of Escherichia coli leader peptidase is necessary, but not sufficient, for its rapid membrane assembly

Leader peptidase of Escherichia coli, a protein of 323 residues, has three hydrophobic domains. The first, residues 1-22, is the most apolar and is followed by a polar region (23-61) which faces the cytoplasm. The second hydrophobic domain (residues 62-76) spans the membrane. The third hydrophobic domain, which has a minimal apolar character, and the polar, carboxyl-terminal two-thirds of the protein are exposed to the periplasm. Deletion of either the amino terminus (residues 4-50) or the third hydrophobic region (residues 83-98) has almost no effect on the rate of leader peptidase membrane assembly, while the second hydrophobic domain is essential for insertion (Dalbey, R., and Wickner, W. (1987) Science 235, 783-787). To further define the roles of these domains, we have replaced the normal, cleaved leader sequence of pro-OmpA and M13 procoat with regions containing either the first or second apolar domain of leader peptidase. The second apolar domain supports the translocation of OmpA or coat protein across the plasma membrane, establishing its identity as an internal, uncleaved signal sequence. In addition to this sequence, we now find that leader peptidase needs either the amino-terminal domain or the third hydrophobic domain to permit its rapid membrane assembly. These results show that, although a signal sequence is necessary for rapid membrane assembly of leader peptidase, it is not sufficient.

[Benign and malignant granular cell tumors. An immunohistochemical classification of tumor cells]

Eight benign and three malignant granular cell tumors were characterized by means of antibodies and antisera against keratin, desmin, epithelial membrane antigen, factor VIII-related protein, lysozyme, myelin basic protein, myoglobin, neurone-specific enolase, S 100 protein, myelin-associated protein (Leu 7), glial fibrillary acidic protein, vimentin, and neurofilament. All benign granular cell tumours showed positive staining of the tumor cells to antibodies against vimentin, S 100 protein, and neurone-specific enolase; myelin-associated protein (Leu 7), in contrast, was only detectable in a few tumor sections. Histogenetically the granular cells may be classified as Schwann's cells which lost their expression of laminin. The three malignant granular cell tumors showed a staining pattern significantly different from that of the benign tumours. Thus, only neurone-specific enolase was detectable in all the tumors, whereas S 100 protein and vimentin could not be demonstrated but in one and two, resp., out of three tumors.

Recombinant forms of M13 procoat with an OmpA leader sequence or a large carboxy-terminal extension retain their independence of secY function

The assembly of phage M13 procoat protein into the plasma membrane of Escherichia coli is independent of the secY protein. To test whether this is caused by the unusually small size of procoat, we fused DNA encoding 103 amino acids to the carboxy-terminal end of the procoat gene. The resulting fusion protein, which attains the same membrane-spanning conformation as mature coat protein, still does not require the secY function for membrane assembly. To determine whether the leader sequence governs interaction with the secY protein, we genetically exchanged the leader peptides between procoat and pro-OmpA, a protein which does require secY for its membrane assembly. Each of the resulting hybrid proteins assembles across the plasma membrane, though at a reduced rate. Membrane assembly of the fusion of procoat leader and OmpA required secY function, whereas assembly of the pro-OmpA leader/coat protein fusion was independent of secY. Properties of the entire procoat molecule, rather than its small size or a specific property of its leader peptide determines its mode of membrane assembly.

[Immunohistologic differential diagnosis of skin tumors in routinely embedded paraffin sections]

Thirty-nine skin tumors of epithelial, mesenchymal, and neuroectodermal origin were studied using antibodies against intermediate filaments and other cell proteins. Formol-fixed and paraffin-embedded material was reconstituted and stained with antibodies against epithelial cells (keratin, epithelial membrane antigen, carcinoembryonic antigen), mesenchymal and histiocytic cells (vimentin, alpha-1-antichymotrypsin, alpha-1-antitrypsin, lysozyme), nerve tissue (neurofilament, glial fibrillary acidic protein, myelin basic protein, myelin-associated protein, neuron-specific enolase), vessels (factor-VIII-related protein), basal cell lamina (laminin) and S-100 protein. Tumor cells displayed the same antibody pattern found in the normal cell type. It is recommended that immunotyping be started with three antibodies to allow gross classification into epithelial (keratin positive), mesenchymal (vimentin positive) and neuroectodermal (vimentin and S-100 protein positive) tumors; then, in a second step, the tumors can be subclassified by the other more specific antibodies listed above. All antibodies used in this study are commercially available and provide reliable results.