Gouy shift and temporal reshaping of focused single-cycle electromagnetic pulses

We discuss exact solutions of Maxwell's equations that describe the evolution of single-cycle electromagnetic pulses. The solutions are applied to recent observations of the diffraction transformation of terahertz pulses. In particular, we elucidate the role of the Gouy shift in the temporal reshaping and polarity reversals of single-cycle terahertz pulses.

Characterization of a 200 kDa glycoprotein (Cs-gp200) on the pathogenic piscine haemoflagellate Cryptobia salmositica

The 200 kDa antigenic doublet of the pathogenic haemoflagellate Cryptobia salmositica Katz, 1951, was detected using a monoclonal antibody (MAb-001) in 1-dimensional SDS-PAGE. This antigenic doublet is a glycoprotein since it was susceptible to both protease K and to sodium m-periodate oxidation and is designated Cs-gp200. It has a PI (isoelectric point) value of about 5.5 (using 2-dimensional gel electrophoresis). It migrated faster under reducing conditions than under nonreducing conditions and was partitioned into the aqueous phase in Triton X-114 phase separation. It is a secretory-excretory product since it was detected in a non-protein culture medium with C. salmositica. These results suggest that the Cs-gp200 is a glycoprotein consisting of carbohydrate determinants and conformational polypeptide with internal disulphide bonds. It is a hydrophilic antigen, is a secretory product of the parasite, and plays a important role in antibody elicitation in immunized fish.

Direct activation of inward rectifier potassium channels by PIP2 and its stabilization by Gbetagamma

Inward rectifier K+ channels, which modulate electrical activity in many cell types, are regulated by protein kinases, guanine-nucleotide-binding proteins (G proteins) and probably actin cytoskeleton. Generation of phosphatidylinositol 4,5-bisphosphate (PIP2) by ATP-dependent lipid kinases is known to activate inward rectifier K+ channels in cardiac membrane patches. Here we report that several cloned inward rectifier K+ channels directly bind PIP2, and that this binding correlates with channel activity. Application of ATP or PIP2 liposomes activates the cloned channels. Stabilized by lipid phosphatase inhibitors, PIP2 antibodies potently inhibit each channel with a unique rate (GIRK1/4 approximately GIRK2 >> IRK1 approximately ROMK. Consistent with the faster dissociation of PIP2 from the GIRK channels, the carboxy terminus of GIRK1 binds 3H-PIP2 liposomes more weakly than does that of IRK1 or ROMK1. Mutation of a conserved arginine to glutamine at position 188 reduces the ability of ROMK1 to bind PIP2 and increases its sensitivity to inhibition by PIP2 antibodies. Interactions between GIRK channels and PIP2 are modulated by the betagamma subunits of the G protein (Gbetagamma). When GIRK1/4 channels are allowed to run down completely, they are not activated by addition of Gbetagamma alone, but application of PIP2 activates them in minutes without Gbetagamma and in just seconds with Gbetagamma. Finally, coexpression of Gbetagamma with GIRK channels slows the inhibition of K+ currents by PIP2 antibodies by more than 10-fold. Thus Gbetagamma activates GIRK channels by stabilizing interactions between PIP2 and the K+ channel.

Biochemical characterisation of an epitope on the surface membrane antigen (Cs-gp200) of the pathogenic piscine haemoflagellate Cryptobia salmositica Katz 1951

A protective surface antigen (200 kDa) on C. salmositica was detected using a monoclonal antibody (mAb-001). Enzymatic studies on the epitope indicated that it was sensitive to nonspecific protease K and to site-specific trypsin and protease V8 but not to alpha-chymotrypsin. The reactivity of the epitope with mAb-001 was not affected when the antigen was denatured with 8 M urea; however, reduction of the antigen with dithiothreitol destroyed the epitope. The epitope was susceptible to sodium m-periodate oxidation and N-glycosidase F, but not to O-glycosidase or neuraminidase. It was also sensitive to mild potassium hydrochloride hydrolysis and to phospholipase C, which is specific for phosphatidylinositol. These results suggest that the epitope consists of a polypeptide, a carbohydrate, and probably a phospholipid. The asparagine-bound N-glycosidically linked hybrid-type carbohydrate chain has the minimum length of a chitobiose core unit. There is probably a phosphatidylinositol residue which anchors the polypeptide to the surface membrane. The antigen is extensively posttranslationally modified.

Fibroblast growth factor receptor 2 limits and receptor 1 accelerates tumorigenicity of prostate epithelial cells

Progressive loss of the differentiated phenotype and communication with stroma accompanies the transition of nonmalignant rat prostate epithelial cells to anaplastic, malignant tumors. Here we show that cell surface expression of the fibroblast growth factor receptor 2 (FGFR2) tyrosine kinase is reduced in malignant tumor cell populations (type II) and undetectable at the mRNA level in 30% of cells. This is in addition to the irreversible loss by splice switching of the FGFR2 ectodomain that abrogates response to FGF-7 and homologues from the stroma. One hundred % of type II malignant cells express FGFR1, which is normally expressed in the stroma. Expression of the FGFR1 kinase in premalignant type I tumor epithelial cells by transfection accelerated progression to the malignant phenotype. In contrast to the FGFR2 kinase fused to the ectodomain of FGFR1, the FGFR1 kinase failed initially to support a mitogenic response to FGF-2 in type I tumor cells. However, the FGFR1-transfected cells acquired a mitogenic response after extensive proliferation of the cell population. Resident FGFR2 and ectopic FGFR1 appeared to be partitioned in the type I cells, because neither full-length nor truncated isoforms of FGFR1 affected the mitogenic response of the other. Restoration of the FGFR2IIIb kinase to malignant cells expressing FGFR1 depressed tumor growth rates, restored responsiveness to stromal cells, and restored epithelial cell differentiation. These observations reveal that homologous FGFR1 and FGFR2 kinases play very different roles in cell growth and differentiation and in development and support of the malignant phenotype.

Laparoscopic cecal ligation and puncture in the rat. Surgical technique and preliminary results

BACKGROUND

We describe a technique of laparoscopic cecal ligation and puncture (CLP) in the rat analogous to open CLP which may facilitate the study of minimally invasive surgery (MIS) and peritonitis.

METHODS

Forty-four rats were randomized to either laparoscopic or open CLP and their 3-day mortality was recorded. Autopsies were performed for peritoneal fluid cultures, measurement of the length of ligated cecum, and scoring of the degree of cecal necrosis.

RESULTS

Laparoscopic CLP required slightly longer operating times compared to open CLP (average 15.6 vs 13.1 min, p = 0.002). Three-day postoperative mortality was 36.4% and 22.7% for open and laparoscopic CLP, respectively (p = NS). There were no differences in the length of ligated cecum or the cecal necrosis score between the open and laparoscopic CLP groups.

CONCLUSION

Laparoscopic CLP is feasible and produces a fecal peritonitis with similar characteristics to those of traditional open CLP.

Borrelia burgdorferi strain-specific Osp C-mediated immunity in mice

Antibodies to the outer surface proteins (Osps) A, B, and C of the spirochete Borrelia burgdorferi can prevent infection in animal models of Lyme borreliosis. We have previously demonstrated that immune serum from mice infected with B. burgdorferi N40 can also prevent challenge infection and induce disease regression in infected mice. The antigens targeted by protective and disease-modulating antibodies are presently unknown, but they do not include Osp A or Osp B. Because Osp C antibodies are present in immune mouse serum, we investigated the ability of hyperimmune serum to recombinant Osp C (N40) to protect mice against challenge infection with N40 spirochetes. In both active and passive immunization studies, Osp C (N40) antiserum failed to protect mice from challenge infection with cultured organisms. Mice actively immunized with recombinant Osp C (N40) were susceptible to tick-borne challenge infection, and nymphal ticks remained infected after feeding on Osp C-hyperimmunized mice. In contrast, similar immunization studies performed with Osp C (PKo) antiserum prevented challenge infection of mice with a clone of PKo spirochetes pathogenic for mice. Both Osp C (N40) and Osp C (PKo) antisera showed minimal in vitro borreliacidal activity, and immunofluorescence studies localized Osp C beneath the outer membrane of both N40 and PKo spirochetes. We conclude that Osp C antibody-mediated immunity is strain specific and propose that differences in Osp C surface expression by spirochetes in vivo may account for strain-specific immunity.

Complement fixing antibody production in thymectomized Oncorhynchus mykiss, vaccinated against or infected with the pathogenic haemoflagellate Cryptobia salmositica

Short-term thymectomized (two months after thymectomy) adult rainbow trout, Oncorhynchus mykiss (Walbaum) infected with the flagellate Cryptobia salmositica Katz, 1951 responded well during primary infection with C. salmositica and recovered fish also showed secondary response (rapid production of complement fixing antibody after homologous challenge) five months after recovery. Complement fixing antibody was detected during primary and secondary responses and the titres of complement fixing antibody in thymectomized fish were significantly lower than those in infected intact fish. The parasitaemia in thymectomized infected fish was significantly lower than in intact infected fish. Both recovered thymectomized fish and intact fish were protected from cryptobiosis when they were challenged. Similarly, long-term thymectomized fish (nine months after thymectomy) vaccinated with an attenuated strain of C. salmositica were protected from cryptobiosis. There were no significant difference (P > 0.05) in parasitaemia, packed cell volume and complement fixing antibody titres between vaccinated/challenged thymectomized and vaccinated/challenged intact fish. Hence, thymectomy in adult rainbow trout did not decrease the detectable complement fixing antibody against C. salmositica in long-term thymectomized fish but reduced the detectable protective antibody in short-term thymectomized fish.

A homeo-interaction sequence in the ectodomain of the fibroblast growth factor receptor

Interaction of fibroblast growth factor receptors (FGFR) sufficient for a trans-phosphorylation event in which one intracellular domain is substrate for the other is essential for signal transduction. By analysis of the direct interaction of recombinant constructions co-expressed in baculoviral-infected insect cells, we identified a 17-amino acid sequence that is required for the stable interaction between ectodomains of FGFR. The sequence 160ERSPHRPILQAGLPANK176 (Glu160-Lys176) connects immunoglobulin modules II and III. In insect cells, the interaction between Glu160-Lys176 domains occurs independently of intact heparin or FGF binding domains. The sequence is not required for the binding of heparin or FGF-1, but is essential for mitogenic activity of the FGFR kinase in mammalian cells. The results support a model in which the homeo-interaction between Glu160-Lys176 in the ectodomain contributes to the interaction between intracellular domains in mammalian cell membranes (Kan, M., Wang, F., Kan, M., To, B., Gabriel, J. L., and McKeehan, W. L. (1996) J. Biol. Chem. 271, 26143-26148). We propose that the Glu160-Lys176 domain plays a pivotal role in restriction of the interaction between kinases by pericellular matrix heparan sulfate proteoglycan and divalent cations. Restrictions are overcome by FGF or constitutively by diverse gain of function mutations which cause skeletal and craniofacial abnormalities.

A sensitive GC-MS procedure for the analysis of flunitrazepam and its metabolites in urine

Analysis of urine specimens collected from individuals ingesting 2 and 4 mg flunitrazepam (FN) showed positive results by OnLine and OnTrak immunoassays for up to 60 h. Gas chromatographic-mass spectrometric (GC-MS) analysis of these specimens for FN, 3-OH-FN, 7-amino-FN, 7-amino-3-OH-FN, desmethyl-FN, and 3-OH-desmethyl-FN after glucuronidase treatment showed only low levels of 7-amino-FN with almost none of the other metabolites. These levels were far below the expected results based on the immunoassay data. This study reports on a GC-MS procedure for FN and the previously listed metabolites. The method is based on acid hydrolysis of the urine specimens, which converts FN and all its metabolites described previously to one of four amino-benzophenone derivatives (1-4) with oxazepam-d5 as the internal standard. Under the experimental conditions, the internal standard is converted to 2-amino-5-chloro-benzophenone-d5. The limit of detection for 7-amino-FN and 7-amino-desmethyl-FN and their 3-OH derivatives was less than 1 ng/mL. Analysis of urine specimens collected for 72-h postingestion of 1, 2, or 4 mg FN showed appreciable levels of benzophenone 3 (product of 7-amino-FN and 7-amino-3-OH-FN) and lower levels of benzophenone 4 (product of 7-amino-desmethyl-FN and 7-amino-3-OH-desmethyl-FN) with no detectable levels of benzophenones 1 and 2. The method makes it possible to confirm the presence of FN metabolites in urine at least 72-h postingestion of small doses of the drug.

Flunitrazepam excretion patterns using the Abuscreen OnTrak and OnLine immunoassays: comparison with GC-MS

A study was conducted to compare the performance of the OnLine and OnTrak immunoassays for benzodiazepines with gas chromatographic-mass spectrometric (GC-MS) analysis in detecting flunitrazepam (FNP) and its metabolites in human urine. Urine was collected over a 72-h period from six individuals (four male and two female) who had taken a single oral dose of either 1 or 4 mg of FNP. The OnTrak assay was run at a 100-ng/mL cutoff of nordiazepam (NDP), and the OnLine assay was run with a standard curve from zero to 200 ng/mL of NDP with and without beta-glucuronidase treatment. Each sample was analyzed by GC-MS using FNP, 7-amino-FNP, 3-hydroxy-FNP, desmethyl-FNP, 7-amino-3-hydroxy-FNP, and desmethyl-3-hydroxy-FNP as standards with beta-glucuronidase treatment. The specimens from the 1-mg dose did not yield a positive result by immunoassay over the 72-h collection period. Specimens from the 4-mg dose did yield positive results in both immunoassays. The time of the first positive result ranged from 4 to 12 h, and the time to the last positive result ranged from 18 to 60 h. Treatment of the samples with beta-glucuronidase increased the OnLine values between 20 and 60%, but it did not appreciably increase the detection time. GC-MS analysis showed no detectable levels of FNP, 3-hydroxy-FNP, desmethyl-FNP, 7-amino-3-hydroxy-FNP, and desmethyl-3-hydroxy-FNP. However, all samples collected past time zero showed detectable levels of 7-amino-FNP (> 2 ng/mL) with peak concentrations at 12-36 h. The peak levels of 7-amino-FNP by GC-MS paralleled the peak levels of the immunoassay response. The amount of 7-amino-FNP metabolite quantitated by GC-MS, however, accounted for only 15-20% of the total immunoassay crossreactive FNP metabolites.

Relationship of necrosis to organ failure in severe acute pancreatitis

BACKGROUND & AIMS

Pancreatic necrosis and organ failure are principal determinants of severity in acute pancreatitis. The purpose of this study was to determine the relationship of necrosis to organ failure in severe acute pancreatitis.

METHODS

Patients with necrotizing pancreatitis from May 1992 to January 1996 were retrospectively studied. Pancreatic necrosis was identified by characteristic findings on dynamic contrast-enhanced computerized tomography scan and infected necrosis by computerized tomography-guided percutaneous aspiration. Organ dysfunction was defined in accordance with the Atlanta symposium.

RESULTS

Organ failure was present in only 26 of 51 patients (51%). There was no difference in the prevalence of organ failure in infected necrosis compared with sterile necrosis (approximately 50% in both groups). Patients with increased amounts of necrosis did not have an increased prevalence of organ failure or infected necrosis compared with those with lesser amounts of necrosis. Patients with organ failure had an increased morbidity and mortality compared with those without organ failure.

CONCLUSIONS

Organ failure occurred in only one half of patients with necrotizing pancreatitis. Because organ failure increases the severity of illness, studies of patients with necrotizing pancreatitis must stratify for organ failure to facilitate interpretation of results.

[The killing effect of IL-2 and IFN-alpha activated bone marrow on K562 leukemic cell]

OBJECTIVE

To evaluate the killing effect of IL-2 and IFN-alpha activated bone marrow cells on K562 cells.

METHODS

Semi-solid colony assay was used.

RESULTS

Bone marrow from leukemia patients in remission was activated in vitro with IL-2 for 3 days. The activated bone marrow (ABM) displayed killing effects of 0.31 approximately 2.30 logs on K562 cells, this killing effects was further increased to 0. 30 approximately > 3.15 logs when IFN-alpha added with IL-2 to the marrow for activation. IL-2 alone or in combination with IFN-alpha showed no inhibition of CFU-GM and K562 cells. Compared with IL-2 or IFN-alpha alone, the combination of the two cytokines could more effectively maintain the killing effect of ABM on leukemic cells.

CONCLUSION

IFN-alpha can augment the purging effect of IL-2 ABM and combination of the two cytokines can effectively maintain the cytotoxicity of ABM.

[Catalytic fluorimetric determination of trace amount of bromine ion]

A new catalytic fluorimetric method for the determination of bromine ion based on its catalytic effect on the oxidation of fluorescein by potassium bromate in the solution of dilute sulfuric acid has been established. The detection limit for Br- is 1.94 x 10(-2) microg/25 mL. The linear range of the determination is 6.0-12.0 microg/25 mL. The method has been applied to the determination of Br- in tablet pyridostigmini bromidum sample with satisfactory results.

[Scopes and applications of LeFort III advancement osteotomy]

In order to correct craniofacial retrusion and malocculusion caused by Crouzon syndrome, we employed LeFort III advancement osteotomies in 21 cases in last 10 years. The differences between craniofacial appearances and cephalometric analyses pre- and postoperatively showed that good results were achieved in all cases. No severe complications in these series were found.

Versatile retrovirus vector systems for regulated gene expression in vitro and in vivo

BACKGROUND

Several plasmid DNA-based mammalian expression systems have recently been developed which make it possible to manipulate gene expression via the administration of exogenous agents. In order to extend the application of these systems, we have developed retroviral vectors which allow for the controlled expression of inserted genes both in vitro and in vivo.

MATERIALS AND METHODS

Two vector strategies which make use of the tetracycline-regulated gene expression system described by Gossen and Bujard were evaluated. In a first strategy, one virus was generated which encoded the tTA or rtTA transactivator gene product, and a second virus was generated in which expression of the gene of interest was dependent upon tetracycline-responsive transcriptional control elements placed either within the viral LTR or within the proviral transcriptional unit. In a second vector strategy, both components of the tet-regulatable system were incorporated into a single proviral genome in such a way that expression of both the transgene and the transactivator gene product were under control of tet-regulatable control elements.

RESULTS

Both vector strategies resulted in the ability to regulate the expression of inserted genes. In one single virus configuration, gene expression could be regulated over 100X and the level of gene expression in the induced state was comparable to or greater than that achieved with standard LTR-based vectors. The use of different deletions in the viral LTR made it possible to generate a number of vectors which provide for a four-fold range of levels of expression of inserted genes in the induced state. Studies in mice with transduced cells demonstrated that gene expression could be induced in vivo by manipulation of tetracycline for at least 48 days.

CONCLUSIONS

The availability of highly transmissible, regulatable retroviral vectors should greatly facilitate studies in which it is of interest to manipulate the expression of specific genes in vitro or in vivo.

Protective and arthritis-resolving activity in sera of mice infected with Borrelia burgdorferi

Transfer of immune serum from immunocompetent mice infected with B. burgdorferi protects mice against syringe challenge, and transfer of immune serum after infection is established induces arthritis resolution but does not clear infection or spirochetemia or resolve carditis. Immune serum had very-high-titer passive protective activity against syringe challenge but failed to protect mice against host-adapted spirochetes when they were challenged with infected tissue transplants. Mice were passively immunized at selected intervals relative to challenge inoculation with antisera to recombinant forms of an immunodominant region of flagellin, P39, and OspC (which are recognized by immune serum), but none provided protection or modified existing infection or disease. Results suggest that spirochetes within joints, but not in other tissues, are selectively vulnerable to immune serum and that immune serum appears to contain antibody against yet-to-be-identified antigens that may be selectively expressed in the context of joint tissue.

[Observation of 212 cases of typhoid fever treated with FQNS]

OBJECTIVES

To treat 212 cases of typhoid fever with Seven kinds of fluoroquinolones (FQNS) and to evaluate their clinical efficacy, bacterial susceptibility and adverse drug reaction (ADR).

METHODS

All the cases were hospitalized and uniantibiotic treated in which NFX group (n = 43) was compared with CP group (n = 28).

RESULTS

204/212 (96.23%) cases were positively cultured. All except 9 (S. paratyphi) were S. typhi. Of the 212 clinically isolated strains, 194(91.51%) were susceptible to FQNS with K-B assay. The MIC except 1 (6.25 mg/L) were all < or = 4 mg/L. The results of MIC detection with 20 strains of clinically isolated bacteria in 1994 and 1995 showed that FQNS were apparently superior to other antityphoid fever antibiotics as chloramphenicol and cefoperazone. When FQNS were used the overall clinical cure rate was 98.11%, the bacterial clear rate was 99.51%, and the rate of ADR was 11.3%. No difference was found between the NFX group and CP group in defervescent days and the cure rates and bacterial carrier state in recovery. The rate of recurrence and ADR in the NFX group was lower than that in the CP group. With the improvement of pharmacokinetics, new FQNS can be administered once or twice a day, and the therapy course shortened from 14 to 7 days. It is considered that FQNS are currently the first choice of antibacterials in treating typhoid fever.

[Effect of bone marrow transplantation conditioning regimen on thyroid and adrenocortical functions in patients with blood diseases]

OBJECTIVE

In order to investigate the life quality of patients with hematological diseases after bone marrow transplantation (BMT).

METHODS

Pituitary-thyroid and adrenocortical function were de tected in 29 patients with hematological diseases before and after BMT.

RESULTS

All patients had normal thyroid and adrenocortical functions before BMT. As compared with pre-BMT,the median serum TSH levels were significantly increased at 3, 6, 12 (P<0.01), 24-60 (P<0.05) months post-BMT. The adrenocortical function had no change in all patients, and thyroid dysfunction were found in 6 of 24 patients detected at a median time of 6 month post-BMT. Five of the 6 thyroid dysfuntion patients developed hypothyroidism, and one hyperthyroidism.

CONCLUSION

There was little effect of conditioning regimen on adrenocortical function, while thyroid dysfunction was common after BMT. Long term follow up on thyroid function in patients after BMT is necessary.

[Determination of degradation level of antifungal agent in mice serum by high performance liquid chromatography]

L-4-oxalysinyl-norvalinyl-N3-4-methoxyfumaroyl-L-2,3-diaminopropanoic acid (I-677-Nva-FMDP) is a new tripeptide synthesized in our group. This peptide exhibits potent anticandida Albicans activity. In the presence of serum, the antifun gal activity of I-677-Nva-FMDP decreases after incubating over 1h. In order to investigate the relationship between the degradation and antifungal activity of I-677-Nva-FMDP, the concentrations of I-677-Nva-FMDP and N3-methoxyfumaroyl-L-2,3-diaminopropanoic acid (FMDP) were determined at different incubating time in mice serum. The incubating time range was from 0 to 300 min and the incubating samples were measured at intervals of 30 min. For this measurement reversed-phase HPLC was used and the mobile phase was composed of 8% methanol and 0.1% trifluoroacitic acid-triethyl amine buffer (pH 3). In this condition the retention time of FMDP and I-677-Nva-FMDP were 3.9 min and 16.5 min respectively. Methanol was superior to other reagents for the removal of protein from the incubating medium and there was not any interference peak before the retention time of I-677-Nva-FMDP. A decrease in concentration of I-677-Nva-FMDP was observed from 0 min to 180 min and no I-677-Nva-FMDP could be detected at 210 min whereas the concentration of FMDP incresed from 30 min to 2h and reached a maximum at 120 min. The results showed that the half life (t1/2) of I-677-Nva-FMDP was 70 min. This result coincided with the antifungal test in vitro.

[In vitro reversal of homoharringtonine resistance by the combination of tamoxifen and verapamil]

OBJECTIVE

To investigate the reversal of homoharringtonine (HHT)-resistance by tamoxifen (TAM) or verapamil (VER) alone or in combination.

METHODS

The drug-sensitivity test was performed with semisolid agar culture.

RESULTS

The cytotoxicity of HHT to K562/S cells was not enhanced by TAM or VER alone or in combination,but HHT resistance in HHT resistant cells (K562/H20) was reversed by VER and TAM at nontoxic doses (4micromol/L or 8micromol/L). The IC50 of K562/H20 for HHT decreased from 446.8 +/- 0.08microg/L to 45.1 +/- 0.02microg/L in the presence of 4micromol/L of VER, to 22.4 +/- 0.03microg/L in 8micromol/L of VER, to 85.1 +/- 0.03microg/L in 4micromol/L of TAM and to 26.4 +/- 0.02microg/L in 8micromol/L of TAM. In the presence of combinations of 2micromol/L VER and 4micromol/L TAM and of 2micromol/L VER and 8micromol/L TAM, IC50 of K562/H20 decreased to 30.4 +/- 0.02microg/L and 4.3 +/- 0.04microg/L, respectively.

CONCLUSION

HHT-resistance could be reversed by VER or TAM alone, and the combination of the two drugs showed a synergistic effect.

A processive versus a distributive mechanism of action correlates with differences in ability of normal and xeroderma pigmentosum group A endonucleases to incise damaged nucleosomal DNA

A DNA endonuclease, isolated from the nuclei of normal human and xeroderma pigmentosum complementation group A (XPA) cells, which recognizes predominately pyrimidine dimers, was examined for the mechanism by which it locates sites of damage on UVC-irradiated DNA. In reaction mixtures with low ionic strengths (i.e. lacking KCl), the normal and XPA endonuclease locate sites of UV damage on both naked and reconstituted nucleosomal DNA by different mechanisms. On both of these substrates, the normal endonuclease acts by a processive mechanism, meaning that it binds non-specifically to DNA and scans the DNA for sites of damage, whereas the XPA endonuclease acts by a distributive one, meaning that it randomly locates sites of damage on DNA. However, while both the normal and XPA endonucleases can incise UVC irradiated naked DNA, they differ in ability to incise damaged nucleosomal DNA. The normal endonuclease showed increased activity on UVC treated nucleosomal DNA compared with naked DNA, whereas the XPA endonuclease showed decreased activity on the damaged nucleosomal substrate. Since a processive mechanism of action is sensitive to the ionic strength of the micro-environment, the KCl concentration of the reaction was increased. At 70 mM KCI, the normal endonuclease switched to a distributive mechanism of action and its ability to incise damaged nucleosomal DNA also decreased. These studies show that there is a correlation between the ability of these endonucleases to act by a processive mechanism and their ability to incise damaged nucleosomal DNA; the normal endonuclease, which acts processively, can incise damaged nucleosomal DNA, whereas the XPA endonuclease, which acts distributively, is defective in ability to incise this substrate.

Regulatory intramolecular association in a tyrosine kinase of the Tec family

The T-cell-specific tyrosine kinase Itk is a member of the Tec family of non-receptor tyrosine kinases, and is required for signalling through the T-cell antigen receptor (TCR). The role of Itk in TCR signalling and the manner in which Itk activity is regulated are not well understood. Substrate binding and enzymatic activity of the structurally related Src kinases are regulated by an intramolecular interaction between the Src-homology-2 (SH2) domain and a phosphotyrosine. Although Itk also contains SH3, SH2 and tyrosine kinase domains, it lacks the corresponding regulatory phosphorylation site, and therefore must be regulated by an alternative mechanism. The proline-rich sequence adjacent to the SH3 domain of Tec family kinases contains an SH3 ligand, potentially allowing a different intramolecular interaction. By using multidimensional nuclear magnetic resonance we have determined the structure of a fragment of Itk, confirming that these domains interact intramolecularly. Formation of this intramolecular SH3-ligand complex prevents the Itk SH3 domain and proline-rich region from interacting with their respective protein ligands, Sam68 and Grb-2. We believe that this structure represents the first example of an intramolecular interaction between an SH3 domain and a proline-rich ligand, and has implications for the regulation of Tec family kinases.