PTPROt-mediated regulation of p53/Foxm1 suppresses leukemic phenotype in a CLL mouse model

The gene encoding PTPROt is methylated and suppressed in Chronic Lymphocytc Leukemia. PTPROt exhibits in vitro tumor suppressor characteristics through the regulation of B-cell receptor signaling. Here, we generated transgenic (Tg) mice with B-cell specific expression of PTPROt. While lymphocyte development is normal in these mice, crossing them with TCL1 Tg mouse model of CLL results in a survival advantage compared to the TCL1 Tg mice. Gene expression profiling of splenic B-lymphocytes before detectable signs of CLL followed by Ingenuity Pathway Analysis revealed that the most prominently regulated functions in TCL1 Tg vs non-transgenic (NTg) and TCL1 Tg vs PTPROt/TCL1 double Tg are the same and also biologically relevant to this study. Further, enhanced expression of the chemokine Ccl3, the oncogenic transcription factor Foxm1 and its targets in TCL1 Tg mice were significantly suppressed in the double Tg mice suggesting a protective function of PTPROt against leukemogenesis. This study also showed that PTPROt mediated regulation of Foxm1 involves activation of p53, a transcriptional repressor of Foxm1, which is facilitated through suppression of B-cell receptor signaling. These results establish the in vivo tumor suppressive function of PTPROt, and identify p53/Foxm1 axis as a key downstream effect of PTPROt-mediated suppression of BCR signaling.

Tumor antigen ROR1 targeted drug delivery mediated selective leukemic but not normal B-cell cytotoxicity in chronic lymphocytic leukemia

Selective cytotoxicity to cancer cells without compromising their normal counterparts pose a huge challenge for traditional drug design. Here we developed a tumor antigen targeted delivery of immunonanoparticle carrying a novel non-immunosuppressive FTY720 derivative OSU-2S with potent cytotoxicity against leukemic B cells. OSU-2S induces activation of protein phosphatase 2A, phosphorylation and nuclear translocation of SHP1^S591 and deregulation of multiple cellular processes in chronic lymphocytic leukemia (CLL) resulting in potent cytotoxicity. To preclude OSU-2S mediated effects on these ubiquitous phosphatases in unintended cells and avoid potential adverse effects we developed a OSU-2S targeted delivery immunonanoparticles (2A2-OSU-2S-ILP), that mediated selective cytotoxicity of CLL but not normal B cells through targeting receptor tyrosine kinase ROR1 expressed in leukemic but not normal B cells. Developing a novel spontaneous CLL mouse model expressing human ROR1 (hROR1) in all leukemic B cells, we demonstrate the therapeutic benefit of enhanced survival with 2A2-OSU-2S-ILP in-vivo. The newly developed non-immunosuppressive OSU-2S, its delivery using human CLL directed immunonanoparticles and the novel transgenic mouse model of CLL that expresses hROR1 exclusively in leukemic B cell surface are highly innovative and can be applied to CLL and other ROR1+ malignancies including mantle cell lymphoma and acute lymphoblastic leukemia.

The LIM protein fhlA is essential for heart chamber development in zebrafish embryos

Four-and-a-half LIM proteins FHL1-3 play important roles in cardiovascular pathophysiology. However, their roles in heart development remain unclear. Here, we report that fhlA, the zebrafish homolog of human FHL1, was found to be expressed around the 22-somite stage. After 24 hpf, expression was restricted to the heart. fhlA knockdown caused an enlarged cardiac chamber phenotype with up-regulated expression of the cardiac markers, but fhlA overexpression reduced the sizes of the cardiac chambers and down-regulated expression of the markers. The morphology associated with the cmlc2, amhc, and vmhc expression patterns at the 22 somite and 24 hpf stages included a broadened domain in embryos lacking fhlA and a smaller domain in embryos overexpressing fhlA. The changes in the sizes of the chambers were attributed to the changes in the number of ventricular and atrial cells. Loss of fhlA caused a longer heart period and pause between heartbeats in M-modes than in controls, but fhlA overexpression caused shorter systolic and diastolic intervals. Abnormal cardiac chambers and physiological function were found to be largely rescued. We also showed the expression of fhlA in the heart to be increased by retinoic acid (RA) and decreased by the RA synthase inhibitor DEAB. Both fhlA and RA signaling caused a phenotype characterized by the morphological alterations in the chamber sizes, suggesting that the role of fhlA in heart development is probably regulated by RA signaling. Taken together, these results showed that fhlA regulates the size of the heart chamber by reducing the number of cardiac cells.

Limb ischemic preconditioning attenuates cerebral ischemic injury in rat model

Ischemic brain injury is not uncommon after open-heart surgery with cardiopulmonary bypass and seriously undermines the patients' life quality. Therefore, potential protective effects of limb ischemic preconditioning (LIP) on subsequent ischemic injury of the brain were investigated by evaluating anti-inflammatory effects and apoptosis of pyramidal neurons in the CA1 hippocampus. One hundred and eight Sprague-Dawley rats were divided into the middle cerebral artery occlusion (MCAO) group (n=54) and the LIP group (n=54). A thread was used to occlude the middle cerebral artery in the MCAO group and the LIP group animals were pretreated with LIP followed by MCAO. In the two groups, nine samples were collected at each time-point of 0, 6, 12, 24, 48 and 72 h after MCAO to detect IL-6 and IL-17 and their mRNA levels. Neurological severity scores (NSS) were examined before the animals were sacrificed. Compared with the LIP group, cerebral histopathological changes in the MCAO group were most distinct and significantly more infiltrated inflammatory and apoptotic neuronal cells were observed at 24, 48 and 72 h post-surgery. IL-17 and IL-6 mRNA levels analyzed by quantitative real-time polymerase chain reaction (PCR) (qRT-PCR) were significantly reduced in the LIP group compared with the MCAO group at the 12, 24 and 48 h time-points. A significant reduction in IL-17 expression level was determined by enzyme-linked immunosorbent assay (ELISA) in the LIP group at 12, 24 and 48 h, while IL-6 was significantly reduced at the 24 and 48 h time-points. The NSSs were not significantly different between the groups. Therefore, in a MCAO rat model, we have proved that LIP pretreatment can protect the brain from infarction after ischemic injury and induce ischemic tolerance, potentially, by reducing IL-17 to provide anti-inflammatory effects and attenuate apoptosis of hippocampal neuronal cells.

Comparative effectiveness of antinociceptive gene therapies in animal models of diabetic neuropathic pain

Peripheral neuropathic pain is one of the most common and debilitating complications of diabetes. Several genes have been shown to be effective in reducing neuropathic pain in animal models of diabetes after transfer to the dorsal root ganglion using replication-defective herpes simplex virus (HSV)1-based vectors, yet there has never been a comparative analysis of their efficacy. We compared four different HSV1-based vectors engineered to produce one of two opioid receptor agonists (enkephalin or endomorphin), or one of two isoforms of glutamic acid decarboxylase (GAD65 or GAD67), alone and in combination, in the streptozotocin-induced diabetic rat and mouse models. Our results indicate that a single subcutaneous hindpaw inoculation of vectors expressing GAD65 or GAD67 reduced diabetes-induced mechanical allodynia to a degree that was greater than daily injections of gabapentin in rats. Diabetic mice that developed thermal hyperalgesia also responded to GAD65 or endomorphin gene delivery. The results suggest that either GAD65 or GAD67 vectors are the most effective in the treatment of diabetic pain. The vector combinations, GAD67+endomorphin, GAD67+enkephalin or endomorphin+enkephalin also produced a significant antinociceptive effect but the combination did not appear to be superior to single gene treatment. These findings provide further justification for the clinical development of antinociceptive gene therapies for the treatment of diabetic peripheral neuropathies.

SU-E-T-569: A Dosimetric Comparison of Helical Tomotherapy versus Intensity Modulated Proton for Lung Cancer

PURPOSE

To evaluate the dosimetric difference between helical tomotherapy (HT) and intensity modulated proton therapy (IMPT) treatment for lung cancer patients.

METHODS

Five patients treated by HT at University of Wisconsin Carbone Cancer Center were selected. HT plans were generated on TomoTherapy treatment planning station (TomoTherapy Inc., USA). The field widths were set to 2.5 cm for all patients in this study. The IMPT plans were generated using the same planning CT and contours with our in-house treatment planning system. Three to five field spot scanning IMPT were used to deliver uniform doses to the targets while minimizing the irradiated lung volume. The proton spots used has a Gaussian sigma of 6mm and are placed on a rectangular grid. The dose distribution of each proton spot is calculated using a pencil beam algorithm with tissue heterogeneity corrections. All the dosimetric analyses are performed using normalized total dose. Alpha/beta ratios were set to 3 for normal tissues and 10 for tumors.

RESULTS

IMPT plans showed improvement of critical structure avoidance and target dose uniformity for all patients. Reductions in mean lung doses of between 81% to 27% were observed in the IMPT plans relative to the HT. The equivalent uniform dose of the target improved from 49.2 Gy in HT plan to 60.04 Gy in IMPT for patient #2, and equivalent for other cases. The maximum doses to cord were reduced by 20.5 Gy on average using IMPT. In two patient cases, the normal tissue complication probabilities were reduced by 53% and 14% with IMPT.

CONCLUSION

IMPT provides improved dose homogeneity on the target and normal structure sparing compared with HT in the treatment of non-small cell carcinoma in lung. Significant reduction of mean lung dose was demonstrated, as well as toxicity to organs at risk adjacent to the target.

Microarray profiling analysis uncovers common molecular mechanisms of rubella virus, human cytomegalovirus, and herpes simplex virus type 2 infections in ECV304 cells

To study the common molecular mechanisms of various viruses infections that might result in congential cardiovascular diseases in perinatal period, changes in mRNA expression levels of ECV304 cells infected by rubella virus (RUBV), human cytomegalovirus (HCMV), and herpes simplex virus type 2 (HSV-2) were analyzed using a microarray system representing 18,716 human genes. 99 genes were found to exhibit differential expression (80 up-regulated and 19 down-regulated). Biological process analysis showed that 33 signaling pathways including 22 genes were relevant significantly to RV, HCMV and HSV-II infections. Of these 33 biological processes, 28 belong to one-gene biological processes and 5 belong to multiple-gene biological processes. Gene annotation indicated that the 5 multiple-gene biological processes including regulation of cell growth, collagen fibril organization, mRNA transport, cell adhesion and regulation of cell shape, and seven down- or up-regulated genes [CRIM1 (cysteine rich transmembrane BMP regulator 1), WISP2 (WNT1 inducible signaling pathway protein 2), COL12A1 (collagen, type XII, alpha 1), COL11A2 (collagen, type XI, alpha 2), CNTN5 (contactin 5), DDR1 (discoidin domain receptor tyrosine kinase 1), VEGF (vascular endothelial growth factor precursor)], are significantly correlated to RUBV, HCMV and HSV-2 infections in ECV304 cells. The results obtained in this study suggested the common molecular mechanisms of viruses infections that might result in congential cardiovascular diseases.

First Report of a Leaf Spot on Basella alba Caused by a Bipolaris sp. in Florida

Malabar spinach (Basella alba L.) is a fast-growing, perennial vegetable crop grown largely in the tropics of Asia and Africa. This crop is widely used in the cuisine of different regions for its thick, semisucculent leaves, mild flavor, and mucilaginous texture. Leaf spots were observed on both surfaces of symptomatic leaf samples received from a home garden in Homestead, FL in November 2009. The necrotic lesions (up to 2 mm in diameter) were round, semicircular, or irregular-shaped with grayish centers surrounded by dark brown borders. A fungus was consistently isolated from symptomatic tissues on clarified V8 (CV8) agar. Fungal colonies on CV8 agar were black and velvet-like with minimal mycelial growth and conidiophores were dark brown, simple, borne singly or in groups upon the substrate. Conidia were straight, pale to medium golden brown, rounded at the ends with three to six septa, and on average measured 75 × 15 μm (48 to 97 × 9 to 18 μm). Cultural and conidial characteristics of the isolates were closely similar to those of a Bipolaris sp. (1). The internal transcribed spacer (ITS) region (~570 bp) of rDNA was amplified using the primers ITS1/ITS4 and sequenced bidirectionally (GenBank Accession No. JF506092). Subsequent database searches by the BLASTN program indicated that the resulting sequence had a 95% identity over 531 bp with the corresponding gene sequence of Bipolaris portulacae (GenBank Accession No. AY004778.1), a fungal pathogen reported to cause leaf spot on purslane (Portulaca oleracea) (2,3). However, our isolate has consistently smaller conidia and does not match descriptions of B. portulacae (BPI 871173, U.S. National Fungus Collections). The pathogenicity was confirmed through inoculation of healthy Malabar spinach plants with conidia of the isolate reproduced on CV8. Six Malabar spinach plants were inoculated with a suspension containing 1 × 10⁶ conidia per ml and sprayed until runoff (approximately 15 ml per plant) with a handheld pressurized canister. Another six noninoculated plants served as a control. Immediately after inoculation, plants were covered with plastic bags for 24 h to maintain high relative humidity and maintained in a greenhouse under ambient conditions. Ten days after inoculation, the symptoms described above were observed on leaves of all inoculated plants, whereas symptoms did not develop on the control plants. A Bipolaris sp. was reisolated and identified by the above methods, fulfilling Koch's postulates. This pathogenicity test was carried out three times. To our knowledge, this is the first report of a Bipolaris sp. affecting Malabar spinach in Florida. Further work should be conducted to confirm identity of these isolates. Because of limited plantings of Malabar spinach, the economic importance of this disease in Florida is currently not known. Nevertheless, this pathogen poses a threat to the growing market of continuously produced oriental vegetables in Florida. References: (1) J. L. Alcorn. Mycotaxon 39:361, 1990. (2) S. A. Alfieri, Jr. et al. Bull. 14. Index of Plant Diseases in Florida (Revised). Florida Dep. Agric. Consumer Serv., Div. Plant Ind., 1984. (3) D. F. Farr and A. Y. Rossman. Fungal Databases. Systematic Mycology and Microbiology Laboratory. ARS, USDA. Retrieved from http://nt.ars-grin.gov/fungaldatabases/ , 25 January 2010.

Genetic suppression of Akt1 activity aggravates cerebral ischemia/reperfusion injury after deep hypothermic low flow in transgenic mice

OBJECTIVE

We investigated the genetic role of the PI3K/Akt signaling pathway in Akt1 (+/-) mice after cerebral ischemia/reperfusion injury following post-surgery deep hypothermic low flow.

METHODS

3-week-old Akt1 (+/-) and wild-type C57/B6 mice were randomly and equally divided into sham-surgery and surgery groups. Surgery group mice were subjected to gradual body temperature reduction and bilateral common carotid artery occlusion for 120 min at 18.5 ± 0.5 °C, followed by artery reopening and rewarming. Occlusion was not performed in sham-surgery group animals. Regional cerebral blood flow was determined by laser Doppler flowmetry. Using reverse transcriptase-PCR, apoptotic assays, immunohistology, and Western blot analyses, we determined the apoptotic level of cerebral cells and the expression of Akt signaling pathway components.

RESULTS

Regional cerebral blood flow was decreased by ≥ 86% during bilateral common carotid artery occlusion. Akt1 (+/-) mice experienced showed mortality after 24 h of cerebral I/R, and displayed increased numbers of apoptotic cerebral cells and apoptotic protein expression levels. Western analysis revealed Akt1 hypoactivity, which led to less efficient apoptotic signaling pathway inhibition.

CONCLUSION

Akt1 suppresses the mitochondrial apoptosis signaling pathway, and Akt1 haplo-insufficiency exacerbates cerebral ischemia/reperfusion after deep hypothermic low flow conditions in mice. Akt may be a potential molecular therapeutic target for brain protection during surgery in congenital heart disease patients.

Effect of mobile phone intervention for diabetes on glycaemic control: a meta-analysis

AIMS

  To assess the effect of mobile phone intervention on glycaemic control in diabetes self-management.

METHODS

We searched three electronic databases (PubMed, EMBASE and Cochrane Library) using the following terms: diabetes or diabetes mellitus and mobile phone or cellular phone, or text message. We also manually searched reference lists of relevant papers to identify additional studies. Clinical studies that used mobile phone intervention and reported changes in glycosylated haemoglobin (HbA(1c) ) values in patients with diabetes were reviewed. The study design, intervention methods, sample size and clinical outcomes were extracted from each trial. The results of the HbA(1c) change in the trials were pooled using meta-analysis methods.

RESULTS

  A total of 22 trials were selected for the review. Meta-analysis among 1657 participants showed that mobile phone interventions for diabetes self-management reduced HbA(1c) values by a mean of 0.5% [6 mmol/mol; 95% confidence interval, 0.3-0.7% (4-8 mmol/mol)] over a median of 6 months follow-up duration. In subgroup analysis, 11 studies among Type 2 diabetes patients reported significantly greater reduction in HbA(1c) than studies among Type 1 diabetes patients [0.8 (9 mmol/mol) vs. 0.3% (3 mmol/mol); P=0.02]. The effect of mobile phone intervention did not significantly differ by other participant characteristics or intervention strategies.

CONCLUSIONS

  Results pooled from the included trials provided strong evidence that mobile phone intervention led to statistically significant improvement in glycaemic control and self-management in diabetes care, especially for Type 2 diabetes patients.

Binding of platelet glycoprotein Ibbeta through the convex surface of leucine-rich repeats domain of glycoprotein IX

BACKGROUND

The mechanism of assembly of the platelet glycoprotein (GP) Ib-IX complex from GPIbalpha, GPIbbeta and GPIX subunits is not entirely clear. In this complex, ectodomains of both GPIbbeta and GPIX subunits contain two leucine-rich repeats (LRR) and share high sequence similarity. However, they differ noticeably in stability, hampering further analysis of their interaction.

OBJECTIVES AND METHODS

Guided by analysis of the LRR structure, we report a well-folded Ibbeta/IX chimera and its usage in dissecting GPIX function.

RESULTS

In this chimera, three non-contiguous sequences that may constitute the putative convex surface of the GPIbbeta ectodomain are replaced by their GPIX counterparts. Like GPIbbeta but unlike GPIX ectodomain, it can secrete from transfected Chinese hamster ovary cells and fold into a stable conformation. Furthermore, replacing the ectodomain in GPIX with the Ibbeta/IX chimera, but not the GPIbbeta ectodomain, preserved its interaction with GPIbbeta as demonstrated by its native-like GPIbbeta-induced increase in surface expression and coimmunoprecipitation.

CONCLUSIONS

The putative convex surface of the LRR domain in GPIX is sufficient, in the context of full-length subunit, to mediate its association with GPIbbeta.

Determination of NMR interaction parameters from double rotation NMR

It is shown that the anisotropic NMR parameters for half-integer quadrupolar nuclei can be determined using double rotation (DOR) NMR at a single magnetic field with comparable accuracy to multi-field static and MAS experiments. The (17)O nuclei in isotopically enriched l-alanine and OPPh(3) are used as illustrations. The anisotropic NMR parameters are obtained from spectral simulation of the DOR spinning sideband intensities using a computer program written with the GAMMA spin-simulation libraries. Contributions due to the quadrupolar interaction, chemical shift anisotropy, dipolar coupling and J coupling are included in the simulations. In l-alanine the oxygen chemical shift span is 455 +/- 20 ppm and 350 +/- 20 ppm for the O1 and O2 sites, respectively, and the Euler angles are determined to an accuracy of +/- 5-10 degrees . For cases where effects due to heteronuclear J and dipolar coupling are observed, it is possible to determine the angle between the internuclear vector and the principal axis of the electric field gradient (EFG). Thus, the orientation of the major components of both the EFG and chemical shift tensors (i.e., V(33) and delta(33)) in the molecular frame may be obtained from the relative intensity of the split DOR peaks. For OPPh(3) the principal axis of the (17)O EFG is found to be close to the O-P bond, and the (17)O-(31)P one-bond J coupling ((1)J(OP)=161 +/- 2 Hz) is determined to a much higher accuracy than previously.

[Long-term follow-up study on Hunan aqueous drainage implantation for refractory glaucoma]

One hundred and three cases(106 eyes) of refractory glaucoma underwent Hunan aqueous drainage (HAD) implantation from July 1993 to January 1998. The mean period of postoperative follow-up was 32.8 months. The intraocular pressure(IOP) was decreased from preoperative 6.6 +/- 1.8 kPa to postoperative 2.2 +/- 1.4 kPa at the 1st year after surgery. The success rates were 83.8% at the 1st year, 80.4% at the 2nd year, 77.1% at the 3rd year, 71.0% at the 4th year, and 64.3% at the 5th year using Kaplan-Meier lifetable analysis. The neovascular glaucoma had lower success rate. The success rate in 38 patients who were used adjunctively with mitomycin C in the operation was 89.5% at the 1st year. The common complications included early continuous flat anterior chamber, local choroidal detachment, increased IOP, and so on. This study suggests that HAD implantation is an effective method in the treatment of refractory glaucoma in spite of its complications.

Human ribonucleotide reductase M2 subunit gene amplification and transcriptional regulation in a homogeneous staining chromosome region responsible for the mechanism of drug resistance

In our previous publication it was shown that a Gemcitabine-resistant KBGem clone derived from step-wise exposure to Gemcitabine resulted in overexpression of the human Ribonucleotide Reductase M2 subunit (hRRM2) mRNA and protein (Goan et al., 1999). In this study we confirm these results and show that the hRRM2 gene amplification arises in a homogeneous staining region (hsr) derived from chromosome translocation. The hydroxyurea-resistant clone (KBHURs) was studied as a comparison. PCR analysis of the hRRM2 gene promoter confirmed the amplification. Northern and Western blots were further employed to confirm the gene amplification and hRRM2 mRNA and protein expression were compatible with the level of drug resistance. Cells synchronized by serum starvation and then returned to serum-containing growth conditions showed a rapid induction of high levels of transcription of the hRRM2 gene. To clarify whether expression of hRRM2 mRNA was regulated at a transcriptional level, several transcription factors, including AP-1, Sp1, AP-2, CREB, NF-kappa B, and OCT1, were examined by gel-shift assay. Interestingly, the KBGem clone was regulated by different transcription factors than the KBHURs clone. Compared to the wild-type KB cells (KBwt), the KBGem clone exhibited a different binding pattern for Sp1 and NF-kappa B. The KBHURs clone, however, demonstrated a unique binding pattern with AP-1 and CREB, different from the KBwt control as well as the KBGem clone. Therefore, we conclude that the drug-resistant phenotype is associated with human RRM2 gene amplification from a homogeneous staining chromosome region and altered transcription regulation. Each clone demonstrated a unique pattern of transcription factor binding that may play a vital role in the mechanism of drug resistance.

Gene transfer into retinal ganglion cells by in vivo electroporation: a new approach

We developed a new in vivo electroporation method to deliver genes into retinal ganglion cells (RGCs). Efficiency and degree of tissue damage were evaluated using green fluorescent protein (GFP) gene and TUNEL. Soon after the intravitreous injection of the GFP gene, electroporation (five electric pulses of 99 ms duration each and 12V/cm delivered twice 5 min apart) was carried out on the adult rat eyeball with the aid of tweezer-type disc electrodes attached to corneal (cathode) and scleral (anode) surfaces. GFP expression, exhibiting a maximum on day 7, was detectable for up to 21 days. DiI retrograde labeling of RGCs showed that 41.5% of the total ganglion cells in the electroinjected area were GFP-positive. Therefore, this new method may be a useful tool for the delivery of genes into RGCs.

[Effect of tetrandrine on expression of bFGF in lung tissue of rat with chronic hypoxic pulmonary hypertension]

OBJECTIVE

To evaluate effect of tetrandrine (Tet) on chronic hypoxic pulmonary by observing expression of bFGF in lung tissue of rat with chronic hypoxic pulmonary hypertension.

METHODS

30 rats were divided into 3 groups: hypoxia group, hypoxia + Tet group and control group. On the 21st day of hypoxia, the hemodynamic parameters were measured and the intra acinar pulmonary arteries (IAPA) changes were studied under light microscopes. Immunohistochemical staining with monoclonal antibody against human recombinant bFGF was performed in the paraffin section of rat lung.

RESULTS

Tetrandrine could reduce pulmonary artery mean pressure (mPAP) and pulmonary vascular resistance (PVR), (P < 0.01), decrease the expression of bFGF in wall of IAPA, and inhibit hypoxic structural remodeling of IAPA.

CONCLUSION

Tetrandrine could decrease the expression of bFGF in wall of IAPA and in that connection to inhibit remodeling of IAPA and pulmonary hypertension.

A C-terminal region of RAG1 contacts the coding DNA during V(D)J recombination

The site-specific DNA rearrangement process, called V(D)J recombination, creates much of the diversity of immune receptor molecules in the adaptive immune system. Central to this reaction is the organization of the protein-DNA complex containing the proteins RAG1 and RAG2 and their DNA targets. A long-term goal is to appreciate the three-dimensional relationships between the proteins and DNA that allow the assembly of the appropriate reaction intermediates, resulting in concerted cleavage and directed rejoining of the DNA ends. Previous cross-linking approaches have mapped RAG1 contacts on the DNA. RAG1 protein contacts the DNA at the conserved heptamer and nonamer sequences as well as at the coding DNA adjacent to the heptamer. Here we subject RAG1, covalently cross-linked to DNA substrates, to partial cyanogen bromide degradation or trypsin proteolysis in order to map contacts on the protein. We find that coding-sequence contacts occur near the C terminus of RAG1, while contacts made within the recombination signal sequence occur nearer the N terminus of the core region of RAG1. A deletion protein lacking the C-terminal DNA-contacting region is still capable of making the N-terminal contacts. This suggests that the two binding interactions may exist on two separate domains of the protein. A trypsin cleavage pattern of the native protein supports this conclusion. A two-domain model for RAG1 is evaluated with respect to the larger recombination complex.