RNA-catalyzed RNA polymerization: accurate and general RNA-templated primer extension.

The RNA world hypothesis regarding the early evolution of life relies on the premise that some RNA sequences can catalyze RNA replication. In support of this conjecture, we describe here an RNA molecule that catalyzes the type of polymerization needed for RNA replication. The ribozyme uses nucleoside triphosphates and the coding information of an RNA template to extend an RNA primer by the successive addition of up to 14 nucleotides-more than a complete turn of an RNA helix. Its polymerization activity is general in terms of the sequence and the length of the primer and template RNAs, provided that the 3' terminus of the primer pairs with the template. Its polymerization is also quite accurate: when primers extended by 11 nucleotides were cloned and sequenced, 1088 of 1100 sequenced nucleotides matched the template.

Recognition of nucleoside triphosphates during RNA-catalyzed primer extension.

In support of the idea that certain RNA molecules might be able to catalyze RNA replication, a ribozyme was previously generated that synthesizes short segments of RNA in a reaction modeled after that of proteinaceous RNA polymerases. Here, we describe substrate recognition by this polymerase ribozyme. Altering base or sugar moieties of the nucleoside triphosphate only moderately affects its utilization, provided that the alterations do not disrupt Watson-Crick pairing to the template. Correctly paired nucleotides have both a lower K(m) and a higher k(cat), suggesting that differential binding and orientation each play roles in discriminating matched from mismatched nucleotides. Binding of the pyrophosphate leaving group appears weak, as evidenced by a very inefficient pyrophosphate-exchange reaction, the reverse of the primer-extension reaction. Indeed, substitutions at the gamma-phosphate can be tolerated, although poorly. Thio substitutions of oxygen atoms at the reactive phosphate exert effects similar to those seen with cellular polymerases, leaving open the possibility of an active site analogous to those of protein enzymes. The polymerase ribozyme, derived from an efficient RNA ligase ribozyme, can achieve the very fast k(cat) of the parent ribozyme when the substrate of the polymerase (GTP) is replaced by an extended substrate (pppGGA), in which the GA dinucleotide extension corresponds to the second and third nucleotides of the ligase. This suggests that the GA dinucleotide, which had been deleted when converting the ligase into a polymerase, plays an important role in orienting the 5'-terminal nucleoside. Polymerase constructs that restore this missing orientation function should achieve much more efficient and perhaps more accurate RNA polymerization.

[Trisomy 18 anomalies on sonography and calculated risk of chromosomal abnormalities during first trimester].

Trisomy 18 is a chromosomal disorder giving multiple anomalies. Its frequency depends on maternal age. We report a 28-year-old woman in her first pregnancy, who underwent first trimester scanning for screening. Due to increased nuchal translucency and exomphalos, chorionic villous sampling was performed. Cytogenetic diagnosis was trisomy 18 and termination of pregnancy was carried out immediately.

Numerical studies of split-operator finite-difference alternating-direction implicit propagation techniques based on generalized Padé approximants.

We study numerically high-order propagation methods that incorporate representations of the exponential of two noncommuting operators as alternating products of Padé approximants of the individual operators. We demonstrate that these generalized Padé approximants are easily assembled through simple recursions and verify the central fact that their order need be far less than that of the overall method. We then analyze light propagation through an integrated-optic microlens using a sixth-order generalized Padé technique and compare its rate of convergence to that of standard propagation algorithms.

Forward wide-angle light propagation in semiconductor rib waveguides.

We derive and examine a new nonparaxial wide-angle equation for unidirectional light propagation. We then develop a rapid unitary solution procedure utilizing both the split-step fast-Fourier-transform and finite-difference techniques. Our calculated losses for the test case of a strongly guiding semiconductor rib-waveguide Y junction are in good agreement with the results of Fresnel equation methods.

Involvement of the spleen in ovarian adenosquamous carcinoma.

Classification of ovarian tumors according to FIGO does not take into account involvement of spleen. A patient who appears to be the first reported case of widespread carcinoma of the ovary with involvement of the splenic parenchyma is presented.

Detection of IgG and IgA antibodies to Chlamydia trachomatis in sera of patients with chlamydial infections: use of immunoblotting and immunoperoxidase assays.

The immune response to individual structural polypeptides of Chlamydia trachomatis was studied in 75 sera from symptomatic and asymptomatic women with culture-proved genital infections and from apparently healthy women who were culture-negative for C. trachomatis. The immunoblotting technique and the single serovar (L2) inclusion immunoperoxidase assays were used for measurement of the various antibodies. Antibodies to 18 structural polypeptides, ranging in molecular weight from 29 to 204 Kdaltons, were detected by the immunoblotting technique in sera from seropositive women. The immunoperoxidase assay showed that sera with high titers of IgG and IgA antibodies to C. trachomatis reacted with more polypeptides than did sera with low titers in this test. Antibodies to the 60- and 62-Kdalton polypeptides were detected in almost all sera positive for IgG and IgA antibodies, irrespective of chlamydial shedding. About 40% of sera with high IgG and IgA titers reacted with 39-, 57-, 64-, 72-, 86-, 105-, 155-, and 204-Kdalton polypeptides. The prevalence of IgA antibodies to C. trachomatis was higher among women with culture-proved chlamydial infections than among apparently healthy controls.

The setting-up of an ambulatory urologic-gynecologic service. Management of patients and results.

An ambulatory set-up is presented which comprises a simple armamentarium for management of women complaining of urinary stress incontinence. Since history appeared to be not sufficiently reliable for management of patients, diagnosis was based mainly on cystomanometry and radiology. Of 58 women who have completed at least six months of follow-up, 11 had been diagnosed as suffering from detrusor instability (DI) and 47 from genuine stress incontinence (SI). Treatment was medical in the former group and surgical in the latter. Significant or complete relief of symptoms was reported in 91% of the former group and in 81% in the latter.

Evaluation of reliability of history in women complaining of urinary stress incontinence.

It was the aim of this study to evaluate critically the value of history in patients complaining of urinary stress incontinence. Diagnosis was established mainly by radiologic and cystomanometric assessment. History included 21 symptoms subdivided into various items. Only 3 symptoms were proven significant in distinguishing between various diagnostic groups. Assessment of stress incontinence should be regarded as incomplete without other means of evaluation in addition to history.

Artificial hydramnion. A simple method of verifying premature rupture of the membranes.

Accurate diagnosis of premature rupture of the membranes is of paramount importance for proper treatment. Currently available methods of diagnosing this complication of pregnancy are not satisfactory. A new, simple, noninvasive method occludes the amniotic outflow with a cervical cap on the external cervical os, permitting the formation of an artificial hydramnion. Observation of this hydramnion formation using ultrasonography and the release of accumulated amniotic fluid after removal of the cap are strong evidence of the existence of premature rupture of the membranes. We used this method in 17 cases.