Guanine tetraplex formation by short DNA fragments containing runs of guanine and cytosine.

Using CD spectroscopy, guanine tetraplex formation was studied with short DNA fragments in which cytosine residues were systematically added to runs of guanine either at the 5' or 3' ends. Potassium cations induced the G-tetraplex more easily with fragments having the guanine run at the 5' end, which is just an opposite tendency to what was reported for (G+T) oligonucleotides. However, the present (G+C) fragments simultaneously adopted other conformers that complicated the analysis. We demonstrate that repeated freezing/thawing, performed at low ionic strength, is a suitable method to exclusively stabilize the tetraplex in the (G+C) DNA fragments. In contrast to KCl, the repeated freeze/thaw cycles better stabilized the tetraplex with fragments having the guanine run on the 3' end. The tendency of guanine blocks to generate the tetraplex destabilized the d(G5).d(C5) duplex whose strands dissociated, giving rise to a stable tetraplex of (dG5) and single-stranded (dC5). In contrast to d(G3C3) and d(G5C5), repeated freezing/thawing induced the tetraplex even with the self-complementary d(C3G3) or d(C5G5); hence the latter oligonucleotides preferred the tetraplex to the apparently very stable duplex. The tetraplexes only included guanine blocks while the 5' end cytosines interfered neither with the tetraplex formation nor the tetraplex structure

Primary gastric Hodgkin's lymphoma

<p>Abstract</p> <p>Background</p> <p>Primary Hodgkin's disease of the stomach is an extremely rare entity. Nearly all cases of primary gastric lymphoma are of the non-Hodgkin's variety. Diagnoses in such cases are difficult due to considerable histological similarities between the 2 disease entities.</p> <p>Case presentation</p> <p>We report the case of a 77 year old lady with a 1 year history of weight loss and poor appetite. Physical examination was unremarkable. Subsequent multiple upper GI endoscopies revealed a large malignant looking ulcer which was deemed to be histologically benign. Following CT imaging the patient underwent a radical gastrectomy. Postoperatively histology and immunohistochemistry failed to confirm a diagnosis. As such a second opinion was sought. Employing an extended array of immunohistological staining a diagnosis of 'Classical Hodgkin's' disease of the stomach was achieved.</p> <p>Conclusion</p> <p>Our case illustrates the significant difficulties in achieving a rare diagnosis of primary Hodgkin's lymphoma of the stomach. The non-specific nature of symptoms and a lack of histological features make a preoperative diagnosis extremely difficult. While immunohistochemistry is widely employed in aiding the evaluation of such cases, one should be wary of the considerable overlap in differentiating between Hodgkin's and non-Hodgkin's disease entities using this technique.</p