[An abdominal Burkitt's lymphoma in acute phase. Case report]. / Il linfoma di Burkitt a localizzazione addominale con presentazione acuta. Caso clinico.

Burkitt's lymphoma is a highly malignant, aggressive and rapidly growing B-cell neoplasm, which has low long-term survival rates. Abdomen is the most frequent onset site of nonendemic Burkitt's lymphoma. The rapidity of volumetric doubling of this neoplasm frequently justifies an abdominal acute presentation, that may mime other less rare diseases. Symptoms are often misleading and make diagnosis difficult. The aim of this work is to report a case of a 13-year-old boy affected by terminal ileum Burkitt's lymphoma with hepatic metastasis, which initially was mistaken for acute appendicitis complicated by hepatic abscesses and, following a second surgical operation, for terminal-ileum inflammatory bowel disease. The rapidity of growth of this neoplasm justifies the finding, during the second surgical operation, of a mass that was not clinically manifested during first operation, carried out only a week ago. Clinical signs and instrumental investigations were not diagnostic, as well as the literature reports. The role of surgery remains controversial, and is usually limited to collection of specimens for histological diagnosis or to management of acute complications, as in our case report. Mostly treatment protocols are based on chemotherapy, because of the high sensibility of this neoplasm.

Interaction of the beta sliding clamp with MutS, ligase, and DNA polymerase I.

The beta and proliferating cell nuclear antigen (PCNA) sliding clamps were first identified as components of their respective replicases, and thus were assigned a role in chromosome replication. Further studies have shown that the eukaryotic clamp, PCNA, interacts with several other proteins that are involved in excision repair, mismatch repair, cellular regulation, and DNA processing, indicating a much wider role than replication alone. Indeed, the Escherichia coli beta clamp is known to function with DNA polymerases II and V, indicating that beta also interacts with more than just the chromosomal replicase, DNA polymerase III. This report demonstrates three previously undetected protein-protein interactions with the beta clamp. Thus, beta interacts with MutS, DNA ligase, and DNA polymerase I. Given the diverse use of these proteins in repair and other DNA transactions, this expanded list of beta interactive proteins suggests that the prokaryotic beta ring participates in a wide variety of reactions beyond its role in chromosomal replication.

Expression, abundance, and RNA polymerase binding properties of the delta factor of Bacillus subtilis.

The delta protein is a dispensable subunit of Bacillus subtilis RNA polymerase (RNAP) that has major effects on the biochemical properties of the purified enzyme. In the presence of delta, RNAP displays an increased specificity of transcription, a decreased affinity for nucleic acids, and an increased efficiency of RNA synthesis because of enhanced recycling. Despite these profound effects, a strain containing a deletion of the delta gene (rpoE) is viable and shows no major alterations in gene expression. Quantitative immunoblotting experiments demonstrate that delta is present in molar excess relative to RNAP in both vegetative cells and spores. Expression of rpoE initiates from a single, sigmaA-dependent promoter and is maximal in transition phase. A rpoE mutant strain has an altered morphology and is delayed in the exit from stationary phase. For biochemical analyses we have created derivatives of delta and sigmaA that can be radiolabeled with protein kinase A. Using electrophoretic mobility shift assays, we demonstrate that delta binds core RNAP with an apparent affinity of 2.5 x 10(6) M-1, but we are unable to demonstrate the formation of a ternary complex containing core enzyme, delta, and sigmaA.

sigma factor mutations affecting the sequence-selective interaction of RNA polymerase with -10 region single-stranded DNA.

Thesigmasubunit of RNA polymerase determines promoter recognition and catalyzes DNA strand separation. The -35 promoter region is recognized by a helix-turn-helix motif in region 4, while the -10 region is specified, at least in part, by an amphipathic helix in region 2. We have proposed that conserved aromatic residues insigmaregion 2.3 interact with the non-template strand of the -10 element to drive open complex formation. We now report that Bacillus subtilis sigmaA holoenzyme, but neither core nor sigmaA alone, binds with high selectivity to single-stranded (ss) DNA containing the non-template -10 consensus sequence. UV irradiation of holoenzyme-ssDNA complexes efficiently crosslinks sigmaA to DNA and protease mapping supports a primary contact site in or near region 2. Several mutations in sigmaA region 2.3, shown previously to impair promoter melting, affect ssDNA binding: Y184A decreases binding selectivity, while Y189A and W193A decrease the efficiency of photocrosslinking. These results support a model in which these aromatic amino acids are juxtaposed to ssDNA, consistent with their demonstrated role in stabilizing the open complex.

Structural analysis of the Bacillus subtilis delta factor: a protein polyanion which displaces RNA from RNA polymerase.

RNA polymerase from Bacillus subtilis is a complex mixture comprising a common core (beta beta' alpha 2), the 20.4 kDa delta (delta) protein, and of one of several sigma (sigma) specificity factors. The delta protein, together with several truncated variants, has been overproduced and purified from Escherichia coli. It is highly acidic (pI = 3.6) and contains two distinct regions, a 13 kDa amino-terminal domain with fairly uniform charge distribution and a glutamate and aspartate residue-rich carboxyl-terminal region. The purified amino-terminal domain (delta N) contains 32% alpha-helix and 16% beta-sheet, as judged by circular dichroism analysis. In contrast, an 8.5 kDa tryptic fragment containing the carboxyl-terminal region (delta C) is largely unstructured and highly charged (net charge of -47). RNA polymerase purified from a B. subtilis mutant with an insertion in the delta gene (rpoE::cat) contains a truncated delta protein, indicating that the amino-terminal domain is stable in vivo and contains a core-binding function. Addition of delta, but not sigma A or delta N, displaces RNA bound to RNA polymerase in a binary complex. The ability of delta to displace RNA efficiently requires the activities of both the amino-terminal core-binding domain and the polyanionic carboxyl-terminal region. Although delta C can also displace nucleic acids from RNA polymerase, this activity requires the addition of a large molar excess of protein and is relatively non specific in that both DNA and RNA are displaced. This suggests that the function of the amino-terminal domain is to bind and orient the carboxyl-terminal region on the surface of RNA polymerase.