Identification of intermolecular RNA cross-links at the subunit interface of the Escherichia coli ribosome

32P-Labeled 70S ribosomes and polysomes were isolated from cultures of Escherichia coli and treated with the cross-linking reagent bis(2-chloroethyl)methylamine. Intermolecular 16S-23S RNA cross-linked complexes were separated from other products of the cross-linking reactions by a two-step sucrose density gradient centrifugation procedure and subjected to oligodeoxynucleotide-directed partial nuclease digestions with RNase H. Cross-linked RNA fragments released by such directed digests were resolved by two-dimensional gel electrophoresis and analyzed using classical oligonucleotide fingerprinting techniques. Two distinct intermolecular cross-links between the 16S and 23S RNA could be localized in this manner, involving positions 1408-1411 and 1518-1520 in the 16S RNA sequence and positions 1912-1920 in the 23S RNA sequence. These data provide the first direct topographical links between the RNA of the 30S and 50S subunits in the functional ribosome and, together with previous topographical data concerning the three-dimensional folding of the rRNA, demonstrate that there is a tight cluster at the ribosomal interface both of sites implicated in ribosomal function and of posttranscriptionally modified nucleotides in the rRNA.

Hypercalcemia mediated by parathyroid hormone-related protein as an early manifestation of pancreatic adenocarcinoma metastasis: a case report

Humoral hypercalcemia of malignancy (HHM) is a paraneoplastic syndrome rarely associated with pancreatic adenocarcinoma. Parathyroid hormone-related peptide (PTHrP) is the central mediator of this condition. In our patient, hypercalcemia associated with elevated PTHrP was the initial manifestation of metastatic pancreatic adenocarcinoma. Successful palliation of HHM with bisphosphonates and loop diuretics has been previously reported and was effective in our patient. We report the first case of pancreatic adenocarcinoma metastasis after successful resection to present with hypercalcemia.

Direct localization by cryo-electron microscopy of secondary structural elements in Escherichia coli 23 S rRNA which differ from the corresponding regions in Haloarcula marismortui

Insertions were introduced by a two-step mutagenesis procedure into each of five double-helical regions of Escherichia coli 23 S rRNA, so as to extend the helix concerned by 17 bp. The helices chosen were at sites within the 23 S molecule (h9, h25, h45, h63 and h98) where significant length variations between different species are known to occur. At each of these positions, with the exception of h45, there are also significant differences between the 23 S rRNAs of E. coli and Haloarcula marismortui. Plasmids carrying the insertions were introduced into an E. coli strain lacking all seven rrn operons. In four of the five cases the cells were viable and 50 S subunits could be isolated; only the insertion in h63 was lethal. The modified subunits were examined by cryo-electron microscopy (cryo-EM), with a view to locating extra electron density corresponding to the insertion elements. The results were compared both with the recently determined atomic structure of H. marismortui 23 S rRNA in the 50 S subunit, and with previous 23 S rRNA modelling studies based on cryo-EM reconstructions of E. coli ribosomes. The insertion element in h45 was located by cryo-EM at a position corresponding precisely to that of the equivalent helix in H. marismortui. The insertion in h98 (which is entirely absent in H. marismortui) was similarly located at a position corresponding precisely to that predicted from the E. coli modelling studies. In the region of h9, the difference between the E. coli and H. marismortui secondary structures is ambiguous, and the extra electron density corresponding to the insertion was seen at a location intermediate between the position of the nearest helix in the atomic structure and that in the modelled structure. In the case of h25 (which is about 50 nucleotides longer in H. marismortui), no clear extra cryo-EM density corresponding to the insertion could be observed.

Aspirin (5 mmol/L) inhibits leukocyte attack and triggered reactive cell proliferation in a 3D human coronary in vitro model

BACKGROUND

Leukocyte attack (LA) and the triggered reactive proliferation of smooth muscle cells (SMCs) are key events for the development of early atherosclerosis and restenosis. In the present study, we used a 3D human coronary in vitro model of LA (3DLA model) to examine the effect of high-dose aspirin on the adhesion and chemotaxis of leukocytes and the reactive proliferative response of SMCs.

METHODS AND RESULTS

For dose-finding, the effect of aspirin (1, 2, 5, and 10 mmol/L) on the tumor necrosis factor-alpha-induced upregulation of intercellular adhesion molecule-1 was analyzed in monocultures of human coronary endothelial cells (HCAEC) and the SMCs of the human coronary media (HCMSMC). In cytoflow and Northern blot experiments, the expression of intercellular adhesion molecule-1 was slightly reduced after incubation with 5 mmol/L aspirin, and strong inhibition was found after incubation with 10 mmol/L. In 3DLA models, HCAECs and HCMSMCs were cultured on both sides of a porous filter. For LA, human monocytes or CD4(+) lymphocytes were seeded on the HCAEC side of the 3DLA unit. A dose of 5 mmol/L aspirin inhibited the adherence of monocytes or CD4(+) lymphocytes by 50% (P:<0.01) and the chemotaxis of monocytes by 90% (P:<0.01). The reactive proliferative response of cocultured HCMSMCs after LA, as measured by the uptake of bromodeoxyuridine, was significantly reduced by 83% after selective monocyte attack (P:<0.001) and by 42% after selective CD4(+) lymphocyte attack (P:<0.05).

CONCLUSIONS

A local concentration of 5 mmol/L aspirin should be accepted as the lowest rational concentration for the beneficial in vitro effects of high-dose aspirin to be reproduced in clinical studies.

The environment of 5S rRNA in the ribosome: cross-links to 23S rRNA from sites within helices II and III of the 5S molecule

Three contiguous fragments of Escherichia coli 5S rRNA were prepared by T7 transcription from synthetic DNA templates. The central fragment, comprising residues 33-71 of the molecule, was transcribed in the presence of 4-thiouridine triphosphate together with [32P]UTP. The three transcripts were ligated together, yielding a 5S rRNA analogue carrying 4-thiouridine residues at positions 40, 48, 55 and 65 in helices II and III. After ligation, the 4-thiouridine residues were derivatised with p -azidophenacyl bromide. The modified 5S rRNA was reconstituted into 50S subunits and these subunits were used to prepare 70S ribosomes in the presence or absence of tRNA and mRNA. The azidophenyl groups were then photoactivated by mild irradiation at 300 nm and the products of cross-linking analysed by our standard procedures. Multiple cross-links from 5S rRNA to two distinct regions of the 23S rRNA were observed. The first region was located in helix 38 in Domain II of the 23S molecule, with cross-links at sites between nucleotides 885 and 922. The second region covered helices 81-85 in Domain V, with sites between nucleotides 2272 and 2345. Taken together with previous data, these results serve to define the arrangement of the 5S rRNA molecule relative to the 23S rRNA within the 50S subunit.

Benzofuro[3,2-b]pyridines as mixed ET(A)/ET(B) and selective ET(B) endothelin receptor antagonists

The discovery, synthesis and structure-activity relationships of a series of novel benzofuro[3,2-b]pyridines as non-selective endothelin ET(A)/ET(B) as well as selective ET(B) receptor antagonists are described. The most potent non-selective inhibitor 7s displayed an IC50 of 21 nM and 41 nM for ET(A) and ET(B) receptors, respectively, whereas 7ee merely showed affinity for the ET(B) receptor (IC50 = 3.6 nM).

Expression of intercellular adhesion molecule-1 in human coronary endothelial and smooth muscle cells after stimulation with tumor necrosis factor-alpha

BACKGROUND

The intercellular adhesion molecule-1 (ICAM-1) is one of several human cell adhesion molecules that play a critical role in the early stages of postangioplasty restenosis. In this study, the in-vitro expression of ICAM-1 in human coronary endothelial cells and human coronary smooth muscle cells (SMC) after stimulation with tumor necrosis factor-alpha (TNF-alpha) was investigated.

METHODS AND RESULTS

SMC were isolated from the media of normal human coronary arteries (n = 26) up to 10 h post mortem (HCMSMC) and from human atherosclerotic coronary arteries (HCPSMC) that were extracted by thrombendarterectomy (n = 25). Endothelial cells of human coronary arteries (HCAEC) were purchased from Clonetics (Cell System, Remagen, Germany), and endothelial cells from human umbilical cord veins (HUVEC) were isolated after vaginal delivery. For investigations of the effect of TNF-alpha (2.5, 5, 10, and 20 ng/ml) on the proliferative activity of HUVEC, HCAEC, HCPSMC, and HCMSMC, serum-free media was used. After 24 h cell number and cell size distribution were measured in a cell analyzer system. The proliferation of HCPSMC and HCMSMC was increased by TNF-alpha; however, significant differences compared with controls were not reached. The proliferation of HUVEC and HCAEC was significantly reduced by TNF-alpha. For investigations of the effect of TNF-alpha (2.5, 5, 10, and 20 ng/ml) on the surface expression of ICAM-1, monoclonal anti-ICAM-1 antibodies (84H10) were used. The expression of ICAM-1 was analyzed using an immunofluorescence microscope. For flow cytometry analysis, 5 x 10(3) cells (100% gated) were analyzed using a fluorescence-activated cell sorter. In control cultures with no stimulation, the expression of ICAM-1 was positive in HCAEC, HCPSMC, HCMSMC, and HUVEC. TNF-alpha stimulated the expression of ICAM-1 in a time- and dose-dependent manner. After maximal stimulation with TNF-alpha (20 ng/ml for 24 h), the expression of ICAM-1 was stronger in HCMSMC than in HCPSMC.

CONCLUSIONS

These results suggest that the cytokine TNF-alpha regulates the expression of ICAM-1 in both human coronary endothelial cells and SMC, and could therefore play an important role in the pathophysiology of inflammatory and immune processes in restenosis after angioplasty.

Endothelin antagonists: discovery of EMD 122946, a highly potent and orally active ETA selective antagonist

The discovery, in vitro and in vivo studies of the highly potent ETA antagonist EMD 122946 are presented. This compound displayed high binding affinity and functional antagonism [IC50 = 3.2 x 10(-11) M, pA2 = 9.5 (ETA)] and inhibited the ET-1 induced pressor response in pithed rats with an ED50 of 0.3 mg/kg. In conscious spontaneously hypertensive rats and in DOCA-salt hypertensive rats the compound lowered mean blood pressure with an ED50 of 0.06 mg/kg. EMD 122946 exhibited high bioavailability in rats and monkeys.

Endothelin antagonists: search for surrogates of methylendioxyphenyl by means of a Kohonen neural network

The methylendioxyphenyl group, present in a number of potent endothelin receptor antagonists, could have undesirable metabolic interactions with cytochrome P450 in vivo. Using a self-organizing neural network we analysed the features of molecular electrostatic potentials of several endothelin receptor ligands. A library of small "fragments and functional groups" together with their corresponding Kohonen maps was generated. By means of this Kohonen map library we discovered the benzothiadiazole group as a surrogate for methylendioxyphenyl.

Endothelin antagonists: evaluation of 2,1,3-benzothiadiazole as a methylendioxyphenyl bioisoster

The methylendioxyphenyl group is present in a number of endothelin receptor antagonists thus far reported. By means of a Kohonen neural network we discovered with a benzothiadiazole a bioisosteric replacement instead. This group should be devoid of the negative metabolic interactions with cytochrome P450 ascribed to methylendioxyphenyl in vivo. The synthesis of a potent benzothiadiazole analogue EMD 122801 together with in vitro studies of different methylendioxyphenyl, benzothiadiazole and benzofurazan derivatives is described.

The ribosomal environment of tRNA: crosslinks to rRNA from positions 8 and 20:1 in the central fold of tRNA located at the A, P, or E site

The naturally occurring nucleotide 3-(3-amino-3-carboxy-propyl) uridine ("acp3U") at position 20:1 of lupin tRNAMet was coupled to a photoreactive diazirine derivative. Similarly, the 4-thiouridine at position 8 of Escherichia coli tRNAPhe was modified with an aromatic azide. Each of the derivatized tRNAs was bound to E. coli ribosomes in the presence of suitable mRNA analogues, under conditions specific for the A, P, or E sites. After photoactivation of the diazirine or azide groups, the sites of crosslinking from the tRNAs to 16S or 23S rRNA were analyzed by our standard procedures, involving a combination of ribonuclease H digestion and primer extension analysis. The crosslinked ribosomal proteins were also identified. The results for the rRNA showed a well-defined series of crosslinks to both the 16S and 23S molecules, the most pronounced being (1) an entirely A-site-specific crosslink from tRNA position 20:1 to the loop-end region (nt 877-913) of helix 38 of the 23S RNA (a region that has not so far been associated at all with tRNA binding), and (2) a largely P-site-specific crosslink from tRNA position 8 to nt 2111-2112 of the 23S RNA (nt 2112 being a position that has previously been identified in footprinting studies as belonging to the ribosomal E site). The data are compared with results from a parallel study of crosslinks from position 47 (also in the central fold of the tRNA), as well as with previously published crosslinks from the anticodon loop (positions 32, 34, and 37) and the CCA-end region (position 76, and the aminoacyl residue).

The ribosomal neighbourhood of the central fold of tRNA: cross-links from position 47 of tRNA located at the A, P or E site

The naturally occurring nucleotide 3-(3-amino-3-carboxy-propyl)uridine (acp3U) at position 47 of tRNA(Phe) from Escherichia coli was modified with a diazirine derivative and bound to ribosomes in the presence of suitable mRNA analogues under conditions specific for the ribosomal A, P or E sites. After photo-activation at 350 nm the cross-links to ribosomal proteins and RNA were identified by our standard procedures. In the 30S subunit protein S19 (and weakly S9 and S13) was the target of cross-linking from tRNA at the A site, S7, S9 and S13 from the P site and S7 from the E site. Similarly, in the 50S subunit L16 and L27 were cross-linked from the A site, L1, L5, L16, L27 and L33 from the P site and L1 and L33 from the E site. Corresponding cross-links to rRNA were localized by RNase H digestion to the following areas: in 16S rRNA between positions 687 and 727 from the P and E sites, positions 1318 and 1350 (P site) and 1350 and 1387 (E site); in the 23S rRNA between positions 865 and 910 from the A site, 1845 and 1892 (P site), 1892 and 1945 (A site), 2282 and 2358 (P site), 2242 and 2461 (P and E sites), 2461 and 2488 (A site), 2488 and 2539 (all three sites) and 2572 and 2603 (A and P sites). In most (but not all) cases, more precise localizations of the cross-link sites could be made by primer extension analysis.

Getting closer to an understanding of the three-dimensional structure of ribosomal RNA

Two experimentally unrelated approaches are converging to give a first low-resolution solution to the question of the three-dimensional organization of the ribosomal RNA from Escherichia coli. The first of these is the continued use of biochemical techniques, such as cross-linking, that provide information on the relative locations of different regions of the RNA. In particular, recent data identifying RNA regions that are juxtaposed to functional ligands such as mRNA or tRNA have been used to construct improved topographical models for the 16S and 23S RNA. The second approach is the application of high-resolution reconstruction techniques from electron micrographs of ribosomes in vitreous ice. These methods have reached a level of resolution at which individual helical elements of the ribosomal RNA begin to be discernible. The electron microscopic data are currently being used in our laboratory to refine the biochemically derived topographical RNA models.

The decoding region of 16S RNA; a cross-linking study of the ribosomal A, P and E sites using tRNA derivatized at position 32 in the anticodon loop

A photo-reactive diazirine derivative was attached to the 2-thiocytidine residue at position 32 of tRNA(Arg)I from Escherichia coli. This modified tRNA was bound under suitable conditions to the A, P or E site of E.coli ribosomes. After photo-activation of the diazirine label, the sites of cross-linking to 16S rRNA were identified by our standard procedures. Each of the three tRNA binding sites showed a characteristic pattern of cross-linking. From tRNA at the A site, a major cross-link was observed to position 1378 of the 16S RNA, and a minor one to position 936. From the P site, there were major cross-links to positions 693 and to 957 and/or 966, as well as a minor cross-link to position 1338. The E site bound tRNA showed major cross-links to position 693 (identical to that from the P site) and to positions 1376/1378 (similar, but not identical, to the cross-link observed from the A site). Immunological analysis of the concomitantly cross-linked ribosomal proteins indicated that S7 was the major target of cross-linking from all three tRNA sites, with S11 as a minor product. The results are discussed in terms of the overall topography of the decoding region of the 30S ribosomal subunit.

Site-directed cross-linking studies on the E. coli tRNA-ribosome complex: determination of sites labelled with an aromatic azide attached to the variable loop or aminoacyl group of tRNA

tRNA(Phe) from E. coli, modified with the photoreactive label N-(p-azidobenzoyl)-glycine (ABG) either at the naturally occurring nucleotide 3-(3-amino-3-carboxy-propyl) uridine (acp3U47) or the alpha-amino group of Phe-tRNA(Phe), was bound nonenzymatically to 70S ribosomes in the presence of poly (U) or short synthetic mRNA molecules prepared by T7 transcription. The noncovalent complexes were subjected to a mild ultraviolet irradiation treatment and the sites of photo-incorporation were analysed. When the photo-affinity label was attached to the aminoacyl group cross-linking was observed from both A- and P-site bound tRNA and involved exclusively the 50S subunit. In both cases the major target of cross-linking was a single site in 23S RNA, localized to position A-2439. A lower yield of cross-linking to L27 from both P- and A-sites was also observed. In contrast, cross-linking from the acp3U47 derivative was specific for P-site bound tRNA and involved mainly (but not exclusively) the 50S subunit. In this case rRNA and ribosomal protein were labelled in approximately equal yields, the sites of cross-linking involving A-2309 in 23S RNA and L33. These results are discussed in the light of our present knowledge concerning the structural arrangement of the tRNA-ribosome complex.

Clustering of modified nucleotides at the functional center of bacterial ribosomal RNA

An aryl trifluoromethyl diazirine photoreactive derivative was attached to the 2-thiocytidine residue at position 32 of tRNA(IArg) and this derivatized tRNA was bound to Escherichia coli 70S ribosomes. After irradiation at 350 nm the site of cross-linking to the 16S RNA was analyzed by our standard procedures and found to lie within the secondary structural element comprising bases 956-983; this region contains two modified nucleotides at positions 966 and 967. Similarly, an aryl azido photoreactive derivative was attached to the phenylalanine residue of Phe-tRNA(Phe), and the derivatized aminoacyl tRNA was bound to the ribosome either at the A- or the P-site. In both cases, after irradiation at 250 nm, the cross-link site was localized to position 2439 of the 23S RNA; in the secondary structure of the latter the neighboring nucleotide 2442 is base-paired to a modified nucleotide at position 2069. Taken together with other cross-linking data, these results now directly implicate a total of 27 out of the 29 modified nucleotides in E. coli 16S and 23S RNA as lying within or close to the functional center of the ribosome.

Localization of a series of RNA-protein cross-link sites in the 23S and 5S ribosomal RNA from Escherichia coli, induced by treatment of 50S subunits with three different bifunctional reagents

50S ribosomal subunits were reacted with bis-(2-chloroethyl)methylamine, 2-iminothiolane or methyl p-azidophenyl acetimidate, and RNA-protein cross-link sites on the RNA were localised using our published procedures. The degree of precision with which these sites could be determined was variable, depending on the particular protein or RNA region concerned. The following positions in the 23S RNA were identified as encompassing the individual cross-link sites (numbered from the 5'-end, with asterisks denoting sites previously reported): L1, 1864-67, 1876-78, 2119-33, 2163-72*, L2, 1819-20*; L3, 2832-34; L4, 320-25*; 613-17*; L5, 2307; L6, 2473-81*; L9, 1484-91; L11, 1060-62; L13, 547-50; L14, 1993-2002; L17, 1260-95; L18, 2307-20; L19, 1741-58; L21, 544-48*; 1198-1248; L23, 63-65, 137-41*; L24, 99-107*; L27, 2272-83, 2320-23*; 2332-37*; L28, 195-242, 368-424; L29, 101-02*; L30, 931-38; L32, 2878-90; L33, 2422-24. Cross-links to 5S RNA were observed with L5 (positions 34-41), and L18 (precise site not localised).

The three-dimensional structure and function of Escherichia coli ribosomal RNA, as studied by cross-linking techniques

A large number of intra-RNA and RNA-protein cross-link sites have been localized within the 23S RNA from E. coli 50 S ribosomal subunits. These sites, together with other data, are sufficient to constrain the secondary structure of the 23 S molecule into a compact three-dimensional shape. Some of the features of this structure are discussed, in particular, those relating to the orientation of tRNA on the 50 S subunit as studied by site-directed cross-linking techniques. A corresponding model for the 16S RNA within the 30 S subunit has already been described, and here a site-directed cross-linking approach is being used to determine the path followed through the subunit by messenger RNA.

Selective isolation and detailed analysis of intra-RNA cross-links induced in the large ribosomal subunit of E. coli: a model for the tertiary structure of the tRNA binding domain in 23S RNA

Intramolecular RNA cross-links were induced within the large ribosomal subunit of E. coli by mild ultraviolet irradiation. Regions of the 23S RNA previously implicated in interactions with ribosomal-bound tRNA were then specifically excised by addressed cleavage using ribonuclease H, in conjunction with synthetic complementary decadeoxyribonucleotides. Individual cross-linked fragments within these regions released by such 'directed digests' were isolated by two-dimensional gel electrophoresis and the sites involved in the cross-links determined using classical oligonucleotide analysis techniques. Using this approach, seven 'new' cross-links could be precisely localised, between positions 1782 and 2608-2609, 1940 and 2554, 1941-1942 and 1964-1965, 1955 and 2552-2553, 2145-2146 and 2202, 2518-2519 and 2544-2545, and between positions 2790-2791 and 2892-2895 in the 23S RNA sequence. These data, in conjunction with data from RNA-protein cross-linking studies carried out in our laboratory, were used to define a model for the tertiary organisation of the tRNA binding domain of 23S RNA 'in situ', in which the specific nucleotides associated with tRNA binding in the 'A' and 'P' sites are clustered at the base of the 'central protuberance' of the 50S subunit.

RNA-protein cross-linking in Escherichia coli 50S ribosomal subunits; determination of sites on 23S RNA that are cross-linked to proteins L2, L4, L24 and L27 by treatment with 2-iminothiolane

RNA-protein cross-links were introduced into E. coli 50S ribosomal subunits by treatment with 2-iminothiolane followed by mild ultraviolet irradiation. After partial digestion of the RNA, the cross-linked RNA-protein complexes were separated by our recently published three-step procedure. In cases where this separation was inadequate, a further purification step was introduced, involving affinity chromatography with antibodies to the ribosomal 50S proteins. Analysis of the isolated complexes enabled four new cross-link sites on the 23S RNA to be identified, as well as re-confirming several previously established sites. The new sites are as follows: Protein L2 is cross-linked within an oligonucleotide at positions 1818-1823 in the 23S RNA, protein L4 within positions 320-325, protein L24 within positions 99-107, and protein L27 within positions 2320-2323.

RNA-protein cross-linking in Escherichia coli 30S ribosomal subunits; determination of sites on 16S RNA that are cross-linked to proteins S3, S4, S7, S9, S10, S11, S17, S18 and S21 by treatment with bis-(2-chloroethyl)-methylamine

RNA-protein cross-links were introduced into E. coli 30S ribosomal subunits by treatment with bis-(2-chloroethyl)-methylamine. After partial nuclease digestion of the RNA moiety, a number of cross-linked RNA-protein complexes were isolated by a new three-step procedure. Protein and RNA analysis of the individual complexes gave the following results: proteins S4 and S9 are cross-linked to the 16S RNA at positions 413 and 954, respectively. Proteins S11 and S21 are both cross-linked to the RNA within an oligonucleotide encompassing positions 693-697, and proteins S17, S10, S3 and S7 are cross-linked within oligonucleotides encompassing positions 278-280, 1139-1144, 1155-1158, and 1531-1542, respectively. A cross-link to protein S18 was found by a process of elimination to lie between positions 845 and 851.

RNA-protein cross-linking in Escherichia coli 30S ribosomal subunits; determination of sites on 16S RNA that are cross-linked to proteins S3, S4, S5, S7, S8, S9, S11, S13, S19 and S21 by treatment with methyl p-azidophenyl acetimidate

RNA-protein cross-links were introduced into E. coli 30S ribosomal subunits by treatment with methyl p-azidophenyl acetimidate. After partial nuclease digestion of the RNA moiety, a number of cross-linked RNA-protein complexes were isolated by a new three-step procedure. Protein and RNA analysis of the individual complexes gave the following results: Proteins S3, S4, S5 and S8 are cross-linked to the 5'-terminal tetranucleotide of 16S RNA. S5 is also cross-linked to the 16S RNA within an oligonucleotide encompassing positions 559-561. Proteins S11, S9, S19 and S7 are cross-linked to 16S RNA within oligonucleotides encompassing positions 702-705, 1130-1131, 1223-1231 and 1238-1240, respectively. Protein S13 is cross-linked to an oligonucleotide encompassing positions 1337-1338, and is also involved in an anomalous cross-link within positions 189-191. Protein S21 is cross-linked to the 3'-terminal dodecanucleotide of the 16S RNA.

The tertiary folding of Escherichia coli 16S RNA, as studied by in situ intra-RNA cross-linking of 30S ribosomal subunits with bis-(2-chloroethyl)-methylamine

Intra-RNA cross-links were introduced into E. coli 30S ribosomal subunits by treatment with bis-(2-chloroethyl)methylamine. The subunits were partially digested with cobra venom nuclease, and the cross-linked complexes were separated by two-dimensional electrophoresis and analysed according to our published procedures. Tertiary structural cross-links in the 16S RNA were identified between nucleotides 31 and 306, and between the tetranucleotide 693-696 and nucleotides 794 or 799. Secondary structural cross-links, lying at the ends of double-helical regions, were found between nucleotides 46 and the trinucleotide 362-364, and between the dinucleotide 148-149 and nucleotide 174. Cross-links within double-helical elements were identified between the tetranucleotide 128-131 and nucleotide 232, between nucleotide 250 and the dinucleotide 274-275, and between nucleotides 1413 and 1486. Adenine as well as guanine residues were involved in the cross-links.

[Haemodialysis in acute renal failure; technique and surveillance (author's transl)]

Access to the blood stream for haemodialysis is generally via an arterio-venous shunt. Experience has shown that the introduction of two Shaldon catheters (with a modified Seldinger technique) into the upper caval system does not require special surgical knowledge and shortens and simplifies the preparations for haemodialysis in acute renal failure. As the catheters can easily be changed over guide wires, correction of obstructions and bacteriological examinations of the catheter tips do not present a problem. There were no complications. With this simplified access the acute stage of renal failure can be bridged for up to 6--8 weeks. The diameter of the catheters ensures an adequate flow of 150--200 ml/min. In vitro tests with a modified catheter (not yet available commercially) established 1. that the flow rate could be increased by 45 percent without altering the pressure of the return flow, and 2. that its use did not increase the rate of haemolysis. Incorrect placing of the catheters--the venous limb should be higher, i.e. nearer the heart, than the "arterial" catheter--may raise the re-circulating fraction by 6--18 percent. Since heparinization is necessary for haemodialysis but carries the grave risk of haemorrhages, espeically in the patients of an intensive care unit, it is essential to provide the means for estimating partial thromboplastin time at the bed side. This allows the heparin doses to be sufficiently reduced to obviate haemorrhage during and after haemodialysis.

Growth hormone release during sleep and with thermal stimulation in depressed patients

The pattern of human growth hormone (HGH) release was studied in depressed patients during sleep under EEG control and employing high temperature exposure. The patients were free of drugs and were compared with corresponding control groups. In the sleep study (6 depressed patients), 2 patients showed no definite increase in HGH plasma concentration, and 3 patients showed an increase in HGH only in the second half of the night, independent of slow wave sleep (SWS). But sleep disturbances were present in all 5 patients. A correlation between SWS and HGH release was found in only 1 patient. One nondepressed control, without SWS, showed a delayed HGH response. Exposure to high temperature in normal subjects induced an acute HGH release. 8 of the 13 patients studied had a deficient HGH RESPONSE. All were depressive, with psycho motor retardation and marked vital and neurovegetative disturbances. These findings support the idea that, at least in a high percentage of depressed patients, there is a disturbance of the hypothalamic pituitary function.