Conformational changes induced in the human protein translin and in the single-stranded oligodeoxynucleotides d(GT)(12) and d(TTAGGG)(5) upon binding of these oligodeoxynucleotides by translin.

Translin is a human single-stranded DNA and RNA binding protein that has been highly conserved in eukaryotic evolution. It consists of eight subunits having a highly helical secondary structure that assemble into a ring. The DNA and the RNA are bound inside the ring. Recently, some of us demonstrated that the human translin specifically binds the single-stranded microsatellite repeats, d(GT)(n), the human telomeric repeats, d(TTAGGG)(n), and the Tetrahymena telomeric repeats, d(GGGGTT)(n). These data suggested that translin might be involved in recombination at d(GT)(n).d(AC)(n) microsatellites and in telomere metabolism. Other data indicated that translin might stimulate binding of telomerase to single-stranded telomeric overhangs by unwinding secondary structures formed by the telomeric repeats. Here we present a circular dichroism (CD) analysis of complexes formed between the human translin and the microsatellite and telomeric oligodeoxynucleotides d(GT)(12) and d(TTAGGG)(5). We report that conformational changes occur in both the translin and the oligodeoxynucleotides upon formation of the complexes. In translin octamers bound to the oligodeoxynucleotide d(GT)(12), the fraction of alpha-helices decreases from approximately 67% to approximately 50%, while the fraction of turns and of the unordered structure increases from approximately 11% to approximately 17% and from approximately 19% to approximately 24%, respectively. In the bound oligodeoxynucleotide d(GT)(12), we observed CD shifts which are consistent with a decrease of base stacking and a putative anti-syn switch of some guanines. The oligodeoxynucleotide d(TTAGGG)(5) formed intramolecular quadruplexes under the conditions of our assays and translin was found to unfold the quadruplexes into structures consisting of a single hairpin and three unwound single-stranded d(TTAGGG) repeats. We suggest that such unfolding could account for the stimulation of telomerase activity by translin mentioned above.

Dense ascites: CT manifestations and clinical implications.

Ascites is a not infrequent finding on CT. Causes of ascites include congestive heart failure, hypoalbuminemia, cirrhosis, inflammation, and neoplasm. In most cases the attenuation of ascites is that of clear fluid, measuring around 0 HU. Rarely, however, a considerably higher density of ascites is seen. This finding may be a challenge for the radiologist, particularly since some of the conditions associated with it are of major clinical importance requiring prompt intervention.

Focal testicular lesion after sperm extraction or aspiration: sonographic appearance simulating testicular tumor.

OBJECTIVE. We describe the sonographic features of focal intratesticular lesions seen in men who underwent sperm retrieval procedures. CONCLUSION. Although many urologists believe that solid intratesticular masses are malignant until proven otherwise, a growing number of benign focal testicular lesions have been described. Awareness of the cause and sonographic appearance of focal abnormalities in men who have undergone testicular aspiration or extraction should help radiologists suggest the correct diagnosis and advise a conservative approach on the basis of close surveillance by serial physical, laboratory, and imaging studies.

Non-neoplastic intratesticular lesions mimicking tumour on ultrasound.

It has recently been emphasized that the incidence of benign testicular lesions is much higher than previously suspected. Sonography is reported to have a high sensitivity but poor specificity in the evaluation of intratesticular abnormalities. This report reviews the common and unusual lesions that can mimic testicular tumour on ultrasound, and discusses the clinical and sonographic features that may help to narrow the differential diagnosis and guide management.

Interference footprinting analysis of telomerase elongation complexes.

Telomerase is a reverse transcriptase that adds single-stranded telomeric repeats to the ends of linear eukaryotic chromosomes. It consists of an RNA molecule including a template sequence, a protein subunit containing reverse transcriptase motifs, and auxiliary proteins. We have carried out an interference footprinting analysis of the Tetrahymena telomerase elongation complexes. In this study, single-stranded oligonucleotide primers containing telomeric sequences were modified with base-specific chemical reagents and extended with the telomerase by a single (32)P-labeled dGMP or dTMP. Base modifications that interfered with the primer extension reactions were mapped by footprinting. Major functional interactions were detected between the telomerase and the six or seven 3'-terminal residues of the primers. These interactions occurred not only with the RNA template region, but also with another region in the enzyme ribonucleoprotein complex designated the telomerase DNA interacting surface (TDIS). This was indicated by footprints generated with dimethyl sulfate (that did not affect Watson-Crick hydrogen bonding) and by footprinting assays performed with mutant primers. In primers aligned at a distance of 2 nucleotides along the RNA template region, the footprints of the six or seven 3'-terminal residues were shifted by 2 nucleotides. This shift indicated that during the elongation reaction, TDIS moved in concert with the 3' ends of the primers relative to the template region. Weak interactions occurred between the telomerase and residues located upstream of the seventh nucleotide. These interactions were stronger in primers that were impaired in the ability to align with the template.

Sonographic features of horseshoe kidney: review of 34 patients.

Horseshoe kidney is a difficult sonographic diagnosis, especially if the isthmus is not seen. The purposes of this report are to review the sonographic images in 34 patients with proven horseshoe kidney, to discuss the limitations of ultrasonography in demonstrating the anomaly, and to identify features that would alert the examiner to the possibility of a horseshoe kidney. Among 34 patients, the isthmus was noted in 27. Of the 67 kidneys studied, 52 (78%) were judged to be low-lying, and in 24 (36%) the sonographic images suggested malrotation with anteriorly pointing pelvis. Additional sonographic features seen in the 67 kidneys included a bent or curved configuration of the kidney in the long axis (58%), tapering and elongation of the lower pole (60%), and a poorly defined inferior border of the kidney (84%). These features should suggest the presence of a horseshoe kidney and direct the examiner to search for the isthmus.

Ureteral catheterization and patient mobilization: is bed restriction mandatory?

OBJECTIVES: We determined whether patient mobilization influences ureteral catheter position in the collecting system. METHODS: 26 consecutive patients (28 renal units) who underwent ureteral catheterization for the purpose of retrograde pyelography or the relief of ureteral obstruction, were included. The position of the catheter's tip within the collecting system and versus the vertebrae was determined for each patient in the baseline supine position; standing upright, and supine again after walking a distance of 5 m. Catheteral displacement was determined by comparing its position in the upright and supine post-walking postures to its original position with the patient supine before any maneuver was undertaken. RESULTS: Assuming the upright position caused an average downward displacement of ureteral catheters by 7.8 mm (ranges 36 mm downward to 14 mm upward displacements, p = 0.0014). In the supine posture following a 5-meter walk, the catheters were downward displaced by 0. 36 mm on average (ranges 12 mm downward and 30 mm upward displacements p = 0.8). None of the ureteral catheters migrated below the uretero-pelvic junction during any phase of the above maneuvers. CONCLUSION: The position of ureteral catheters remains unchanged within the collecting system when patients stand or walk for 5 m. Therefore, mandatory bed restriction is not justified in patients with ureteral catheters.

DNA molecules can drive the assembly of other DNA molecules into specific four-stranded structures.

Single-stranded DNA molecules containing clustered G-repeats can be assembled into various four-stranded structures linked by G-quartets. Here, we report that such molecules can also drive the assembly of other DNA molecules containing G-repeats into specific four-stranded structures. In these assays, the oligonucleotides 5'-CAGGCTGAGCAGGTACGGGGGAGCTGGGGTAGATTGGAATGTAG-3' (oligo D) and 5'-CGGGGGAGCTGGGGT-3' (oligo B), consisting of sequences found in immunoglobulin switch regions, were annealed in a buffer containing K+ and the annealing products were analyzed by polyacrylamide gel electrophoresis. This analysis revealed that whereas annealing of each oligo alone produced four-stranded structures designated D2 and B2, annealing of mixtures containing both oligos produced additional complexes designated D2* and B2*. D2* and B2* were found to contain only D molecules and only B molecules, respectively. The yield of D2* increased and the yield of B2* decreased, as the concentration ratio oligo B/oligo D was increased. These results indicated that B can drive the assembly of D into D2* and D can drive the assembly of B into B2*. Further studies revealed that while the assembly of D2 followed a second order kinetics, the B-driven assembly of D2* followed a first order kinetics. Dimethyl sulfate footprinting indicated that both D2 and D2* are four-stranded structures containing two parallel and two antiparallel chains. In addition, annealing of D mixed with various B mutants showed that only mutants containing two G-clusters can drive the assembly of D2*. Based on these data, we propose that in the process of D2* assembly, a four-stranded intermediate containing B and D is formed and then dissociates into D2* and B in a rate-limiting first order reaction. Driver mechanisms of this type may cause formation of specific four-stranded structures at G-rich chromosomal sites, thereby regulating processes such as recombination and telomere synthesis.

[Epidermoid cyst of the spleen].

Splenic cysts are rarely found or diagnosed. Excluding cases of trauma, the events preceding their development have not been fully understood. We describe a 22-year-old woman in her 34th week of pregnancy in whom ultrasound revealed a cystic lesion 8 x 10 cm. in diameter in the left upper abdomen. Further imaging tests followed by laparotomy confirmed the splenic origin of the cyst. Splenectomy was performed and the lesion was histopathologically defined as an epidermoid cyst.

Sonographic diagnosis of seminal vesicle cysts in autosomal dominant polycystic kidney disease.

Multiple, bilateral seminal vesicle cysts were found in a young man by transabdominal sonography. Examination of the kidneys disclosed previously unknown autosomal dominant polycystic kidney disease. This case report draws attention to the rare association between these 2 conditions.

Transrectal ultrasonographically assisted radical retropubic prostatectomy.

Radical prostatectomy is associated with difficulty in determining the division site of the urethra adjacent to the apical region of the prostate. We present the results of a feasibility clinical trial in three patients to determine whether intraoperative transrectal ultrasonography may assist during radical retropubic prostatectomy. Using this technique the apex is readily identified and a detailed view of the urethral stump could be obtained. In one case residual apical tissue was identified and excised. The creation of the vesicourethral anastomosis was documented and its water tightness was demonstrated. We conclude that transrectal ultrasonography can be performed during radical retropubic prostatectomy and may be helpful in selected cases.

Torsion of the testicular appendages: sonographic appearance.

Torsion of the testis and torsion of the testicular appendages have similar presenting features, namely, acute testicular pain and swelling. The former condition requires urgent surgical intervention to save the testis; the latter condition can be treated conservatively. Despite the frequency of torsion of the appendix testis, which is the most common cause of acute hemiscrotum in the child, only occasional references to this entity are found in the radiological literature. We describe five cases in which an enlarged, homogeneously echogenic appendix testis was seen medial or posterior to the head of the epididymis. All cases were accompanied by hydrocele and thickening of the scrotal wall. Among the five cases, enlargement of the head of the epididymis was seen in four and increased testicular blood flow in two. Scanning in the coronal and transverse planes above the testis was useful in locating the enlarged, twisted appendix.

The SV40 large T-antigen helicase can unwind four stranded DNA structures linked by G-quartets.

We describe a novel activity of the SV40 large T-ag helicase, the unwinding of four stranded DNA structures linked by stacked G-quartets, namely stacked groups of four guanine bases bound by Hoogsteen hydrogen bonds. The structures unwound by the helicase were of two types: (i) quadruplexes comprising four parallel strands that were generated by annealing oligonucleotides including clustered G residues in a buffer containing Na+ions. Each parallel quadruplex consisted of four oligonucleotide molecules. (ii) Complexes comprising two parallel and two antiparallel strands that were generated by annealing the above oligonucleotides in a buffer containing K+ions. Each antiparallel complex consisted of two folded oligonucleotide molecules. Unwinding of these unusual DNA structures by the T-ag was monitored by gel electrophoresis. The unwinding process required ATP and at least one single stranded 3'-tail extending beyond the four stranded region. These data indicated that the T-ag first binds the 3'-tail and moves in a 3'-->5'direction, using energy provided by ATP hydrolysis; then it unwinds the four stranded DNA into single strands. This helicase activity may affect processes such as recombination and telomere extension, in which four stranded DNA could play a role.

[Transrectal ultrasound-controlled needle aspiration of a prostatic cyst].

Prostatic cysts are common and are usually acquired and asymptomatic. Congenital prostatic cysts, which may originate from the wolffian system or from remnants of the Muellerian duct, are rare and may cause obstructive symptoms in young adults. Due to the availability of transrectal ultrasonography an increased number of cases of prostatic cysts are being diagnosed. We report a 36-year-old man with a congenital prostatic cyst which caused increasing pain during ejaculation and decreased the force of the urinary stream. It was diagnosed by ultrasonography and treated successfully by ultrasound-controlled, transrectal needle aspiration. There was immediate, complete disappearance of symptoms and no complications.

Unwinding of the third strand of a DNA triple helix, a novel activity of the SV40 large T-antigen helicase.

We present experiments indicating that the SV40 large T-antigen (T-ag) helicase is capable of unwinding the third strand of DNA triple helices. Intermolecular d(TC)(20)d(GA)(20)d(TC)(20) triplexes were generated by annealing, at pH 5.5, a linearized double-stranded plasmid containing a d(TC)(27).d(GA)27 tract with a (32)P-labeled oligonucleotide consisting of a d(TC)(20) tract flanked by a sequence of 15 nt at the 3'-end. The triplexes remained stable at pH 7.2, as determined by agarose gel electrophoresis and dimethyl sulfate footprinting. Incubation with the T-ag helicase caused unwinding of the d(TC)(20) tract and consequent release of the oligonucleotide, while the plasmid molecules remained double-stranded. ATP was required for this reaction and could not be replaced by the non-hydrolyzable ATP analog AMP-PNP. T-ag did not unwind similar triplexes formed with oligonucleotides containing a d(TC)(20) tract and a 5' flanking sequence or no flanking sequence. These data indicate that unwinding of DNA triplexes by the T-ag helicase must be preceded by binding of the helicase to a single-stranded 3' flanking sequence, then the enzyme migrates in a 3'--> 5' direction, using energy provided by ATP hydrolysis, and causes release of the third strand. Unwinding of DNA triplexes by helicases may be required for processes such as DNA replication, transcription, recombination and repair.

Pyogenic liver abscess: warning indicator of silent colonic cancer. Report of a case and review of the literature.

PURPOSE: Carcinoma of the colon, manifested clinically as an enterococcal hepatic abscess, in the absence of liver metastases, is very uncommon. However, having treated a patient with such a condition, we would like to draw the attention of surgeons to this possibility. Most reports describe secondary infections of hepatic metastases only in patients with a known malignancy. However, increased awareness of colonic cancer as an underlying cause of pyogenic liver abscesses will afford earlier diagnosis and treatment. METHODS: The case was analyzed for history, presentation, laboratory data, radiologic studies, and bacteriology. RESULTS: A 66-year-old woman presented with abdominal pain, fever, and chills. Imaging scans revealed a solitary liver abscess, which was successfully treated with percutaneous drainage and broad-spectrum intravenous antibiotics. Pus cultures grew Streptococcus faecalis. A search for the underlying cause led to the discovery of an adenocarcinoma of the sigmoid colon. CONCLUSIONS: An aggressive search for the underlying cause of pyogenic liver abscesses should be an integral part of the definitive treatment of this disease. After prevailing etiologies have been excluded, silent colonic cancer should be considered.

Intrahepatic abscess due to gallbladder perforation.

BACKGROUND: Perforation of the gallbladder with cholecystohepatic communication is a rare cause of liver abscess. We report four cases of this condition and describe the imaging procedures related to its diagnosis and treatment. METHODS: The medical and x-ray files of 39 patients with percutaneous drainage of liver abscesses were retrospectively reviewed. Four patients with hepatic abscess due to gallbladder perforation were identified. The patients presented with clinical features suggestive of cholecystitis. RESULTS: Sonography in four patients showed a hypoechoic lesion in the liver adjacent to the gallbladder. CT in three patients showed a hypodense area in the liver, corresponding to the sonographic findings. Percutaneous abscess drainage, followed by an abscessogram, was performed in all patients. Contrast material injected through the drainage catheter filled the gallbladder directly from the abscess cavity. Two patients subsequently underwent cholecystectomy, confirming perforation of the gallbladder fundus. In both cases the gallbladder was noted to be embedded in the liver and covered by adhesions. CONCLUSION: Perforation of the gallbladder is a rare cause of pyogenic liver abscess. We suggest, however, based on our two patients who underwent surgery, and several cases reported in the literature, that this condition may be more common when the gallbladder is partially or totally intrahepatic.

Formation of DNA triple helices inhibits DNA unwinding by the SV40 large T-antigen helicase.

Previous studies have indicated that d(TC)n.d(GA)n microsatellites may serve as arrest signals for mammalian DNA replication through the ability of such sequences to form DNA triple helices and thereby inhibit replication enzymes. To further test this hypothesis, we examined the ability of d(TC)i.d(GA)i.d(TC)i triplexes to inhibit DNA unwinding in vitro by a model eukaryotic DNA helicase, the SV40 large T-antigen. DNA substrates that were able to form triplexes, and non-triplex-forming control substrates, were tested. We found that the presence of DNA triplexes, as assayed by endonuclease S1 and osmium tetroxide footprinting, significantly inhibited DNA unwinding by T-antigen. Strong inhibition was observed not only at acidic pH values, in which the triplexes were most stable, but also at physiological pH values in the range 6.9-7.2. Little or no inhibition was detected at pH 8.7. Based on these results, and on previous studies of DNA polymerases, we suggest that DNA triplexes may form in vivo and cause replication arrest through a dual inhibition of duplex unwinding by DNA helicases and of nascent strand synthesis by DNA polymerases. DNA triplexes also have the potential to inhibit recombination and repair processes in which helicases and polymerases are involved.