Continuous interscalene block using a stimulating catheter: a review of the technique

The management of postoperative pain after major shoulder surgery can be achieved successfully with a continuous interscalene block. This article reviews the essentials of the stimulating catheter technique for the continuous interscalene block that was described by Boezaart in 1999. The authors also describe their experience and results with the first two hundred catheters they placed.

Towards integrating vectors for gene therapy: expression of functional bacteriophage MuA and MuB proteins in mammalian cells

Bacteriophage Mu has one of the best studied, most efficient and largest transposition machineries of the prokaryotic world. To harness this attractive integration machinery for use in mammalian cells, we cloned the coding sequences of the phage factors MuA and MuB in a eukaryotic expression cassette and fused them to a FLAG epitope and a SV40-derived nuclear localization signal. We demonstrate that these N-terminal extensions were sufficient to target the Mu proteins to the nucleus, while their function in Escherichia coli was not impeded. In vivo transposition in mammalian cells was analysed by co-transfection of the MuA and MuB expression vectors with a donor construct, which contained a miniMu transposon carrying a Hygromycin-resistance marker (Hyg(R)). In all co-transfections, a significant but moderate (up to 2.7-fold) increase in Hyg(R) colonies was obtained if compared with control experiments in which the MuA vector was omitted. To study whether the increased efficiency was the result of bona fide Mu transposition, integrated vector copies were cloned from 43 monoclonal and one polyclonal cell lines. However, in none of these clones, the junction between the vector and the chromosomal DNA was localized precisely at the border of the Att sites. From our data we conclude that expression of MuA and MuB increases the integration of miniMu vectors in mammalian cells, but that this increase is not the result of bona fide Mu-induced transposition.

Opposite effects of Ras or PKC activation on the expression of the SPRR2A keratinocyte terminal differentiation marker

Epidermal growth factor (EGF) enhances the expression of the keratinocyte terminal differentiation marker SPRR2A, when added to monolayers of basal keratinocytes, induced to stratify by increasing the extracellular calcium concentration. A similar stimulation is found during suspension-induced differentiation in methylcellulose. This effect, which is observed after several hours of EGF addition, is restricted to terminally differentiating keratinocytes and is dependent on PKC signaling. EGF also transiently activates the Ras signaling pathway, with a maximum induction after 10 min (Medema et al., 1994, Mol. Cell. Biol. 14, 7078-7085). The cellular effects of activated Ras were determined by transient transfection of Ha-ras(Leu-61) into normal human keratinocytes. Activated Ras completely inhibited PKC-mediated expression of SPRR2A. This inhibition is mediated via c-Jun as it is reversed by a dominant-negative c-Jun mutant (cJunDelta6/194) and c-Jun can substitute for activated Ras. The inhibitory effect is targeted to a 150-bp minimal promoter region, which is essential and sufficient for SPRR2A expression during keratinocyte terminal differentiation. This indicates that the Ras and PKC pathways, which both can be triggered by EGF, although at different time points, have opposite effects on SPRR2A gene expression.

Structure and evolution of the human SPRR3 gene: implications for function and regulation

SPRR3, a member of the SPRR family of cornified envelope precursor proteins, is expressed in oral and esophageal epithelia, where it is strictly linked to keratinocyte terminal differentiation. This gene is characterized by intragenic duplications that have created the characteristic proline-rich repeats in the coding sequence, an alternative noncoding exon, and a 200-bp polypyrimidine tract in the promoter region. Mutational analysis of the promoter region and transient transfection in normal human keratinocytes showed that in addition to the polypyrimidine tract, multiple regulatory elements are involved in differentiation-specific expression. These elements include a high-affinity Ets binding site bound by ESE-1, an AP-1 site (TRE) recognized by the Jun/Fos family of transcription factors, and an ATF/CRE bound by Jun/Fos and ATF factors. The repositioning of the SPRR3 Ets binding site during evolution has a major effect on the relative contribution of this site to promoter activity.

Involvement of a nuclear matrix association region in the regulation of the SPRR2A keratinocyte terminal differentiation marker

The small proline-rich protein genes ( SPRRs ) code for precursors of the cornified cell envelope, and are specifically expressed during keratinocyte terminal differentiation. The single intron of SPRR2A enhanced the activity of the SPRR2A promoter in transient transfection assays. This enhancement was position dependent, and did not function in combination with a heterologous promoter, indicating that the intron does not contain a classical enhancer, and that the enhancement was not due to the splicing reaction per se. Mild DNAse-I digestion of nuclei showed the SPRR2 genes to be tightly associated with the nuclear matrix, in contrast to the other cornified envelope precursor genes mapping to the same chromosomal location (epidermal differentiation complex). In vitro binding studies indicated that both the proximal promoter and the intron of SPRR2A are required for optimal association of this gene with nuclear matrices. Neither nuclear matrix association nor the relative transcriptional enhancement by the intron changed during keratinocyte differentiation. Apparently, the association of the SPRR2A gene with the nuclear matrix results in a general, differentiation-independent enhancement of gene expression.

AP-1 and ets transcription factors regulate the expression of the human SPRR1A keratinocyte terminal differentiation marker

The 173-base pair proximal promoter of SPRR1A is necessary and sufficient for regulated expression in primary keratinocytes induced to differentiate either by increasing extracellular calcium or by 12-O-tetradecanoylphorbol-13-acetate (TPA) treatment. Whereas calcium-induced expression depends both on an AP-1 and an Ets binding site in this region, responsiveness to TPA resides mainly (but not exclusively) on the Ets element, indicating that Ets factors are important targets for protein kinase C signaling during keratinocyte terminal differentiation. This conclusion is further substantiated by the finding that expression of ESE-1, an Ets transcription factor involved in SPRR regulation, is also induced by TPA, with kinetics similar to SPRR1A. The strict AP-1 requirement in SPRR1A for calcium-induced differentiation is not found for SPRR2A, despite the presence of an identical AP-1 consensus binding site in this gene. Binding site swapping indicates that both the nucleotides flanking the TGAGTCA core sequence and the global promoter context are essential in determining the contribution of AP-1 factors in gene expression during keratinocyte terminal differentiation. In the distal SPRR1A promoter region, a complex arrangement of positive and negative regulatory elements, which are only conditionally needed for promoter activity, are likely involved in gene-specific fine-tuning of the expression of this member of the SPRR gene family.

Regulation of single-strand RNA synthesis of alfalfa mosaic virus in non-transgenic cowpea protoplasts by the viral coat protein

We have compared the RNA synthesis of alfalfa mosaic virus in complete (by RNAs 1, 2 and 3) and incomplete infections (by RNAs 1 and 2) of cowpea protoplasts. Both viral RNA polymerase activity and accumulation of viral RNA were measured. By annealing RNA in solution with 32P-labelled probes of plus and minus polarity followed by treatment with ribonucleases, we determined viral RNAs quantitatively in both single- and double-stranded RNA fractions. The accumulation of single-stranded RNA of positive polarity differed considerably between the two types of infection (250 ng vs. less than 1 ng per 10(5) protoplasts), although viral RNA polymerase activities as measured in vitro and the concentrations of minus RNA were similar. Since the method also measured fragmented RNA, this difference is probably not due to lack of protection of viral RNA by coat protein during incomplete infection. Synthesis of single-stranded plus RNA requires either RNA 3 itself or one of its gene products. We postulate that coat protein is the stringent regulator of alfalfa mosaic virus genomic expression.

Function of the homologous regions of the Escherichia coli DNA excision repair proteins UvrB and UvrC in stabilization of the UvrBC-DNA complex and in 3'-incision

The nicking of damaged DNA during the nucleotide excision repair reaction in E. coli, is the result of a multi-step process involving three enzymes, UvrA, UvrB and UvrC. The UvrB protein is loaded on the site of the damage by UvrA, forming a stable UvrB-DNA complex. This complex is recognized by UvrC and in the resulting UvrBC-DNA complex dual incision takes place, first on the 3'-side and next on the 5'-side of the damaged nucleotide. A domain in the C-terminal part of UvrB has been identified to be essential for formation of the specific UvrBC-DNA complex that induces the 3'-incision [1]. The N-terminal half of UvrC contains a region that is homologous to this C-terminal domain of UvrB. Using site-directed mutagenesis of a conserved phenylalanine in the homologous regions of UvrB and UvrC two mutants were constructed, UvrB(F652L) and UvrC(F223L). Both proteins were tested in vitro using a DNA substrate with a defined cisplatin lesion. The protein-DNA and protein-protein interactions were studied using bandshift assays and DNAse I footprinting. We show that both domains are important for the binding of UvrC to the UvrB-DNA complex.

Transitions in the coupling of transcription and nucleotide excision repair within RNA polymerase II-transcribed genes of Saccharomyces cerevisiae

The molecular mechanism of transcription-coupled nucleotide excision repair in eukaryotes is poorly understood. The identification of the dual role of basal transcription factor TFIIH in DNA repair and transcription provided a plausible link between both processes. However, TFIIH is not part of the elongating transcription complex, suggesting that additional components are required to recruit TFIIH when RNA polymerase II (RNAPII) stalls at the site of DNA damage. Previously, we have shown that the yeast Rad26 protein is involved in transcription-coupled DNA repair. This paper describes the differential contribution of the Rad26 protein to efficient removal of UV-induced cyclobutane pyrimidine dimers (CPDs) from transcribed DNA. Two distinct regions within the transcribed strand of RNAPII-transcribed genes are identified that differ in their requirement for the RAD26 gene product. Using high-resolution repair analysis, we determined the in vivo repair kinetics of cyclobutane pyrimidine dimers positioned around the transcription initiation site of RNAPII-transcribed genes RPB2 and URA3. Although transcription-coupled repair is severely reduced in rad26 mutants, lesions positioned in a small region immediately downstream of transcription initiation are efficiently removed in the absence of Rad26. The observed transition in repair characteristics is abrupt and in excellent agreement with the region where TFIIH dissociates from RNAPII in vitro, strongly suggesting an inverse correlation between TFIIH association and Rad26 requirement. These data suggest that a transcription repair coupling factor (Rad26/CSB) is required for efficient repair only during the elongating stages of RNAPII transcription.

The integration host factor-DNA complex upstream of the early promoter of bacteriophage Mu is functionally symmetric

Inversion of the ihf site in the promoter region of the early promoter of bacteriophage Mu did not influence the integration host factor (IHF)-mediated functions. IHF bound to this inverted site could counteract H-NS-mediated repression, directly activate transcription, and support lytic growth of bacteriophage Mu. This implies that the IHF heterodimer and its asymmetrical binding site form a functionally symmetrical complex.

Transcription elongation factor S-II is not required for transcription-coupled repair in yeast

Two different subpathways play a role in removal of UV-induced cyclobutane pyrimidine dimers (CPDs) by nucleotide excision repair (NER). The relatively slow global genome repair subpathway operates on all CPDs irrespective of their position in the DNA, whereas the transcription-coupled repair subpathway is responsible for the rapid removal of CPDs from transcribed strands. In Saccharomyces cerevisiae, the RAD26 gene is implicated in transcription-coupled repair. However, transcription-coupled repair is not completely absent in rad26 mutants, and therefore other gene products are possibly involved in this subpathway. Based on in vitro experiments with purified components, the transcription elongation factor S-II appeared to be a candidate for a function in transcription-coupled repair. To investigate a possible role of S-II in transcription-coupled repair in vivo in yeast, S-II null mutations were introduced into various genetic backgrounds differing in NER capacity. UV sensitivity was not altered by disruption of the S-II gene in a RAD+ (NER proficient) strain, or in rad26 (impaired in efficient transcription-coupled repair), rad7 (lacking global genome repair), or rad7 rad26 (lacking global genome repair, but having residual transcription-coupled repair capacity) mutants. Moreover, S-II did not influence the repair rate on the transcribed strand of the RPB2 gene, either in repair-proficient or in rad7 rad26 backgrounds. Hence, transcription-coupled repair is fully functional in yeast cells lacking the gene encoding S-II. Furthermore, S-II is not required for the Rad26-independent residual transcription-coupled repair in vivo.

Involvement of c-JUN in the regulation of terminal differentiation genes in normal and malignant keratinocytes

In stratifying cultures of human keratinocytes, expression of the proto-oncoprotein c-JUN and the small proline rich 2 (SPRR2) protein, a precursor of the cornified cell envelope, are inversely related. Whereas c-JUN is typically found in basal proliferating cells, SPRR2 is restricted to suprabasal differentiating layers. Malignant keratinocytes (derived from squamous cell carcinoma, SCC) have reduced sprr2 expression, consistent with their low potential to differentiate, and express c-jun at higher levels than normal keratinocytes. A direct relation between c-jun and sprr2 expression was shown in several ways: transient ectopic expression of c-jun inhibits sprr2a promoter activity in normal differentiating cells, whereas in malignant keratinocytes a dominant negative c-jun mutant restored at least partially both the low promoter activity and the expression of endogenous sprr2. These effects are mediated via a 134 bp promoter fragment which does not include the sprr2a AP-1 binding site. Interestingly, in an SCC cell line, constitutively expressing the dominant c-jun mutant, expression of the terminal differentiation marker involucrin is also strongly increased, suggesting that c-JUN is a general modulator of keratinocyte terminal differentiation rather than only affecting the expression of sprr2.

Expression of the SPRR cornification genes is differentially affected by carcinogenic transformation

The small proline rich protein (SPRR) genes constitute a family of conserved genes which are part of the human epidermal differentiation complex (EDC) on chromosome 1q21 and code for precursor proteins of the cornified cell envelope. The expression of these genes is strictly linked to keratinocyte terminal differentiation both in vivo and in vitro. Here we show that cultured cell lines derived from squamous cell carcinoma (SCC) show significantly lower levels of SPRR expression than normal human keratinocytes. However, the residual SPRR expression in SCC lines appears to be both gene and cell line specific. Expression of SPRR2 appears to correlate well with the residual ability of these cells to differentiate. However, the kinetics of SPRR2 expression, following treatment with calcium, an inducer of keratinocyte differentiation, are typical for each cell line and differ substantially from the ones found in normal cells. In most cell lines a rapid transient expression of SPRR2 contrasts with a slow induction leading to a high sustained level of expression in normal cells. This pattern of expression is typical for SPRR2 and not observed for the other SPRR genes or involucrin. Our analysis indicates that the expression of various keratinocyte terminal differentiation markers, even when involved in the same biological process (cornification), can be differentially affected by carcinogenic transformation.

Function of the C-terminal domain of the alpha subunit of Escherichia coli RNA polymerase in basal expression and integration host factor-mediated activation of the early promoter of bacteriophage Mu

Integration host factor (IHF) can activate transcription from the early promoter (Pe) of bacteriophage Mu both directly and indirectly. Indirect activation occurs through alleviation of H-NS-mediated repression of the Pe promoter (P. Van Ulsen, M. Hillebrand, L. Zulianello, P. Van de Putte, and N. Goosen, Mol. Microbiol. 21:567-578, 1996). The direct activation involves the C-terminal domain of the alpha subunit (alphaCTD) of RNA polymerase. We investigated which residues in the alphaCTD are important for IHF-mediated activation of the Pe promoter. Initial in vivo screening, using a set of substitution mutants derived from an alanine scan (T. Gaal, W. Ross, E. E. Blatter, T. Tang, X. Jia, V. V. Krishnan, N. Assa-Munt, R. Ebright, and R. L. Gourse, Genes Dev. 10:16-26, 1996; H. Tang, K. Severinov, A. Goldfarb, D. Fenyo, B. Chait, and R. H. Ebright, Genes Dev. 8:3058-3067, 1994), indicated that the residues, which are required for transcription activation by the UP element of the rrnB P1 promoter (T. Gaal, W. Ross, E. E. Blatter, T. Tang, X. Jia, V. V. Krishnan, N. Assa-Munt, R. Ebright, and R. L. Gourse, Genes Dev. 10:16-26, 1996), are also important for Pe expression in the presence of IHF. Two of the RNA polymerase mutants, alphaR265A and alphaG296A, that affected Pe expression most in vivo were subsequently tested in in vitro transcription experiments. Mutant RNA polymerase with alphaR265A showed no IHF-mediated activation and a severely reduced basal level of transcription from the Pe promoter. Mutant RNA polymerase with alphaG296A resulted in a slightly reduced transcription from the Pe promoter in the absence of IHF but could still be activated by IHF. These results indicate that interaction of the alphaCTD with DNA is involved not only in the IHF-mediated activation of Pe transcription but also in maintaining the basal level of transcription from this promoter. Mutational analysis of the upstream region of the Pe promoter identified a sequence, positioned from -39 to -51 with respect to the transcription start site, that is important for basal Pe expression, presumably through binding of the alphaCTD. The role of the alphaCTD in IHF-mediated stimulation of transcription from the Pe promoter is discussed.

Cloning of Schizosaccharomyces pombe rph16+, a gene homologous to the Saccharomyces cerevisiae RAD16 gene

The RAD16 gene is involved in the nucleotide excision repair of UV damage in the transcriptional silenced mating type loci (Terleth et al., 1990 and Bang et al., 1992) and in non-transcribed stands of active genes in Saccharomyces cerevisiae (Verhage et al., 1994). Using touchdown-PCR with primers derived from various domains of the S. cerevisiae Rad 16 protein, a specific Schizosaccharomyces pombe probe was isolated. This probe was used to obtain the complete RAD16 homologous gene from a S. pombe chromosomal bank. DNA sequence analysis of the rph16+ gene revealed an open reading frame of 854 amino acids. Comparison of the amino acid sequences of the Rhp16 and Rad16 proteins showed a high level of conservation: 68% similarity. The Rhp16 protein sequence contains the two Zn-finger motifs and the putative helicase domains as found in the Rad16 protein. Like the RAD16, the rph16+ gene is UV-inducible (Bang et al., 1995). In analogy with the rad16 mutant, the rhp16 disruption mutant is viable and grows normally, indicating that the gene does not have an essential function. The rhp16 disruption mutant is not sensitive for UV but is sensitive for cisplatin. The rhp16+ gene cloned behind the GAI 1 promoter partially complements the UV sensitivity and the defect in the non-transcribed strand DNA repair of a S. cerevisiae rad16 mutant, indicating functional homology between the rhp16+ and RAD16 genes. The structural and functional homology between the two genes suggests that the RAD16 dependent subpathway of NER for the repair of non-transcribed DNA is evolutionary conserved.

Transcription-coupled and global genome repair in the Saccharomyces cerevisiae RPB2 gene at nucleotide resolution

Repair of UV-induced cyclobutane pyrimidine dimers (CPDs) was examined at single nucleotide resolution in the yeast Saccharomyces cerevisiae, using an improved protocol for genomic end-labelling. To obtain the sensitivity required for adduct detection in yeast, an oligonucleotide-directed enrichment step was introduced into the current methodology developed for adduct detection in Escherichia coli. With this method, heterogeneous repair of CPDs within the RPB2 locus is observed. Individual CPDs positioned in the transcribed strand are removed very efficiently with identical kinetics. This fast repair starts within 23 bases downstream of the transcription initiation site. The non-transcribed strand of the active gene exhibits slow repair without detectable repair variations between individual lesions. In contrast, CPDs positioned in the promoter region show profound repair heterogeneity. Here, CPDs at specific sites are removed very quickly, with comparable rates to CPDs positioned in the transcribed strand, while at other positions lesions are not repaired at all during the period studied. Interestingly, the fast repair in the promoter region is dependent on the RAD7 and RAD16 genes, as are the slowly repaired CPDs in this region and in the non-transcribed strand. This indicates that the global genome repair pathway is not intrinsically slow and at specific positions can be as efficient as the transcription-coupled repair pathway.

Integration host factor alleviates the H-NS-mediated repression of the early promoter of bacteriophage Mu

Integration host factor (IHF), which is a histone-like protein, has been shown to positively regulate transcription in two different ways. It can either help the formation of a complex between a transcription factor and RNA polymerase or it can itself activate RNA polymerase without the involvement of other transcription factors. In this study, we present a third mechanism for IHF-stimulated gene expression, by counteracting the repression by another histone-like protein, H-NS. The early (Pe) promoter of bacteriophage Mu is specifically inhibited by H-NS, both in vivo and in vitro. For this inhibition, H-NS binds to a large DNA region overlapping the Pe promoter. Binding of IHF to a binding site just upstream of Pe alleviates the H-NS-mediated repression of transcription. This same ihf site is also involved in the direct activation of Pe by IHF. In contrast to the direct activation by IHF, however, the alleviating effect of IHF appears not to be dependent on the relevant position of the ihf site on the DNA helix, and it also does not require the presence of the C-terminal domain of the alpha subunit of RNA polymerase. Footprint analysis shows that binding of IHF to the ihf site destabilizes the interaction of H-NS with the DNA, not only in the IHF-binding region but also in the DNA regions flanking the ihf site. These results suggest that IHF disrupts a higher-order nucleoprotein complex that is formed by H-NS and the DNA.

Comparison of spontaneous hprt mutation spectra at the nucleotide sequence level in the endogenous hprt gene and five other genomic positions

Mutation spectra at the nucleotide sequence level of five hprt cDNA genes integrated in different genomic positions of a HPRT(-) derivative of the human lymphoblastoid TK6 cell line were compared with each other and with the spectrum of mutations confined to the 657 bp coding region of the endogenous hprt gene in the parental TK6 cells. The mutation rates in these genomic positions vary significantly and also the mutation spectra are different. In each genomic position the majority of mutations are basepair substitutions and deletions. the ratios of which vary among the genomic positions. Although it is likely that the different rates of deletion are to a large extent the net result of different rates of misalignment and repair of these errors in the various genomic positions, for the basepair substitutions it is not possible to deduce which mechanisms have caused these mutations and what causes the differences among the genomic positions. Taken together, the differences in mutation rates and spectra cannot be explained by a single mutagenic process.

Analysis of gene- and strand-specific repair in the moderately UV-sensitive Saccharomyces cerevisiae rad23 mutant

The RAD23 gene of Saccharomyces cerevisiae is involved in nucleotide excision repair (NER) and mutations in this gene confer a moderate sensitivity to UV irradiation. However, no repair of either cyclobutane pyrimidine dimers (CPDs) and 6-4 photoproducts, the major types of lesions formed upon UV irradiation, was detectable during the first 4 h post UV irradiation in a rad23 mutant. rad23, like the rad7 and rad16 mutants, is not as UV sensitive as completely NER-deficient mutants. The rad7 and rad16 mutants are only partly defective in NER: non-transcribed strands are completely refractory to repair while transcription-coupled repair is not affected. To investigate whether the rad23 mutant has similar strand-specific repair characteristics we analyzed gene-specific CPD removal from several loci using strand-specific probes but did not detect any repair. The moderate UV sensitivity of rad23 mutants as compared to completely NER-deficient mutants is therefore not due to gene- or strand-specific removal of lesions, indicating that rad23 mutants do not have a similar repair defect as rad7 or rad16 mutants, but are presumably defective in general NER. The rad23 mutation does not suppress the high UV sensitivity of completely NER-deficient rad1 or rad14 strains. This demonstrates that the relatively high survival of rad23 mutants in not due to an increased tolerance for the lesions that seem to persist in the genome but rather requires some NER function.

Double mutants of Saccharomyces cerevisiae with alterations in global genome and transcription-coupled repair

The nucleotide excision repair (NER) pathway is thought to consist of two subpathways: transcription-coupled repair, limited to the transcribed strand of active genes, and global genome repair for nontranscribed DNA strands. Recently we cloned the RAD26 gene, the Saccharomyces cerevisiae homolog of human CSB/ERCC6, a gene involved in transcription-coupled repair and the disorder Cockayne syndrome. This paper describes the analysis of yeast double mutants selectively affected in each NER subpathway. Although rad26 disruption mutants are defective in transcription-coupled repair, they are not UV sensitive. However, double mutants of RAD26 with the global genome repair determinants RAD7 and RAD16 appeared more UV sensitive than the single rad7 or rad16 mutants but not as sensitive as completely NER-deficient mutants. These findings unmask a role of RAD26 and transcription-coupled repair in UV survival, indicate that transcription-coupled repair and global genome repair are partially overlapping, and provide evidence for a residual NER modality in the double mutants. Analysis of dimer removal from the active RPB2 gene in the rad7/16 rad26 double mutants revealed (i) a contribution of the global genome repair factors Rad7p and Rad16p to repair of the transcribed strand, confirming the partial overlap between both NER subpathways, and (ii) residual repair specifically of the transcribed strand. To investigate the transcription dependence of this repair activity, strand-specific repair of the inducible GAL7 gene was investigated. The template strand of this gene was repaired only under induced conditions, pointing to a role for transcription in the residual repair in the double mutants and suggesting that transcription-coupled repair can to some extent operate independently from Rad26p. Our findings also indicate locus heterogeneity for the dependence of transcription-coupled repair on RAD26.

The in vitro more efficiently repaired cisplatin adduct cis-Pt.GG is in vivo a more mutagenic lesion than the relative slowly repaired cis-Pt.GCG adduct

The toxic effect and the mutagenicity of two differentially repaired site-specific cis-diamminedichloroplatinum(II) (cis-DDP) lesions were investigated. Detailed analysis of the UvrABC-dependent repair of the two lesions in vitro showed a more efficient repair of the cis-Pt.GG adduct compared to that of the cis-Pt.GCG adduct (Visse et al., 1994). Furthermore, previously, a dependency of cis-DDP mutagenesis on UvrA and UvrB, but not on UvrC was found (Brouwer et al., 1988). To possibly relate survival and mutagenesis to repair, plasmids containing the same site-specific cis-DDP lesions as those that were used in the detailed repair studies were transformed into Escherichia coli. The results indicate that both lesions are very efficiently bypassed in vivo. Mutation analysis was performed using a denaturing gradient gel electrophoresis technique, which allows identification of mutations without previous selection. Although the cis-Pt.GG adduct is in vitro more efficiently repaired than the cis-Pt.GCG adduct, it appeared to be more mutagenic. We present a model in which this result is related to the previously observed dependency of the mutagenicity of cis-DDP lesions on the Uvr A and B proteins.

The C-terminal region of the UvrB protein of Escherichia coli contains an important determinant for UvrC binding to the preincision complex but not the catalytic site for 3'-incision

The UvrABC endonuclease from Escherichia coli repairs damage in the DNA by dual incision of the damaged strand on both sides of the lesion. The incisions are in an ordered fashion, first on the 3'-side and next on the 5'-side of the damage, and they are the result of binding of UvrC to the UvrB-DNA preincision complex. In this paper, we show that at least the C-terminal 24 amino acids of UvrB are involved in interaction with UvrC and that this binding is important for the 3'-incision. The C-terminal region of UvrB, which shows homology with a domain of the UvrC protein, is part of a region that is predicted to be able to form a coiled-coil. We therefore propose that UvrB and UvrC interact through the formation of such a structure. The C-terminal region of UvrB only interacts with UvrC when present in the preincision complex, indicating that the conformational change in UvrB accompanying the formation of this complex exposes the UvrC binding domain. Binding of UvrC to the C-terminal region of UvrB is not important for the 5'-incision, suggesting that for this incision a different interaction of UvrC with the UvrB-DNA complex is required. Truncated UvrB mutants that lack up to 99 amino acids from the C terminus still give rise to significant incision (1-2%), indicating that this C-terminal region of UvrB does not participate in the formation of the active site for 3'-incision. This region, however, contains the residue (Glu-640) that was proposed to be involved in 3'-catalysis, since a mutation of the residue (E640A) fails to promote 3'-incision (Lin, J.J., Phillips, A.M., Hearst, J.E., and Sancar, A. (1992) J. Biol. Chem. 267, 17693-17700). We have isolated a mutant UvrB with the same E640A substitution, but this protein shows normal UvrC binding and incision in vitro and also results in normal survival after UV irradiation in vivo. As a consequence of these results, it is still an open question as to whether the catalytic site for 3'-incision is located in UvrB, in UvrC, or is formed by both proteins.

Atraumatic cardiac arrest in apparently healthy young women

Sudden non-traumatic death in young people (< 30 years old) has been discussed both in systematic studies and anecdotal reports. After presenting three remarkable cases, a global survey of the incidence with special reference to the Belgian CPCR database, ethiopathogenesis and prognosis of sudden non-traumatic death in this specific age group is given. The atherosclerotic coronary artery disease (CAD) related and especially the non-CAD related causes are extensively discussed as well as the role of intoxication and increasing drug and substance abuse. After conventional cardiopulmonary resuscitation with restoration of spontaneous circulation and a favourable neurological outcome, a thorough search for the underlying disease is mandatory. The involvement of drugs or other toxins has to be excluded in the first place. Apart from transoesophageal echocardiography and coronary angiography, electrophysiological testing, serological exams, myocardial biopsy and magnetic resonance imaging should be considered.