Recombination between repeats in Escherichia coli by a recA-independent, proximity-sensitive mechanism

We have examined the influence of proximity on the efficiency of recombination between repeated DNA sequences in Escherichia coli. Our experiments have employed a plasmid-based assay to detect deletions between direct repeats of 100 bp. The rate of deletion of the juxtaposed direct repeats was reasonably high at 6 × 10^–5 per cell. A comparison of recA+ and recA mutant strains showed that these deletion events are primarily the result of recA-independent recombination at these homologous sequences. Random restriction fragments of yeast or E. coli genomic DNA were used to separate the two repeats. Deletion rates decreased over two orders of magnitude with increasing separation of up to 7 kb. There was a surprisingly strong effect of even short sequence separations, with insertions of a few hundred base pairs exhibiting 10-fold reductions of deletion rates. No effect of recA on the efficiency of deletion was observed at any distance between repeats.     

Reduction of the surface-volume ratio: a physical mechanism contributing to the loss of red cell deformability in malaria

Plasmodia and other intraerythrocytic parasites reduce the deformability of the red cells they infect. One mechanism potentially responsible for this reduction in deformability is the decrease in the surface:volume (S/V) ratio of the red cell which occurs with parasite growth. To examine this hypothesis, normal red cells were allowed to phagocytize polylysine-coated latex spheres 1.0 to 2.9 microns in diameter. Deformability decreased progressively with spheres of increasing size, consistent with the decreasing S/V ratios of those cells (from an initial length:width [L/W] ratio of 2.398 +/- 0.549 for normal red cells to 1.559 +/- 0.249 for red cells containing 2.92 microns latex spheres at 40 dynes per cm2, p less than 0.001). Nevertheless, red cells containing latex spheres 2.0-2.9 microns in diameter remained deformable and continued to tank tread, in contrast to red cells containing Plasmodium falciparum parasites of that size, which are not deformable and do not tank tread. The progressive decrease in S/V produced by the latex spheres is consistent with their effect on the L/W ratio. However, the total loss of deformability observed with red cells containing parasites of similar or smaller size cannot be explained on these grounds alone. It suggests an additional mechanism, such as calcium-induced crosslinking of the red cell cytoskeleton.     

Effect of Lincocin Treatment on the Greening Process in Bean (Phaseolus vulgaris) Leaves

The effect of lincocin (a plastid protein synthesis inhibitor) treatment on the greening process of bean (Phaseolus vulgaris L.) leaves have been studied. In comparison with control leaves treated ones had a decreased rate of chloroplast development. They had a marked chlorophyll deficiency and a decreased chlorophyll a/b ratio. Some long and short wavelength forms of chlorophyll a were lacking as evidenced from the absorption spectra at 25°C and the fluorescence spectra at 77°K. The –¹⁴CO₂ fixation was inhibited by 80–90% in treated leaves. The fluorescence induced by the measuring light was greater in the treated leaves than in the control ones, and the kinetics of the decline of the relative fluorescence intensity were also different. Electron microscopic studies showed macrogranum-like structures and incomplete membrane vesicles in the treated plastids. After longer treatment a destruction of membranes was observed. The results indicate some structural and functional membrane deficiencies and instability of the membranes.     

Accurate determination of mean cell volume by isotope dilution in erythrocyte populations with variable deformability.

Variations in erythrocyte deformability and morphology lead to artifacts in electronic determinations of mean cellular volume (MCV) by the aperture-impedance method. The micropipette-aspiration technique loses accuracy when applied to severely aberrant cells such as dense sickle cells. A new light-scattering technique requires that the cells be capable of undergoing isovolumetric sphering. In contrast, the isotope-dilution (ID) method measures absolute mean volume and is free of artifacts associated with abnormal deformability or morphology. It does not depend on any algorithms or correction factors and does not subject the cells to any stringent processing, not even centrifugation. The ID method can be used to determine the mean volume of red cells in hypo- or hypertonic media or in the presence of pharmacologic agents. It requires no more than a 1-ml aliquot of suspended cells at a hematocrit of at least 30%. The cells can be readily recovered, washed, and reused. Using EDTA labeled with 57Co as an extracellular space marker we have used ID to determine the MCV of fractionated normal human red blood cells (RBC), unfractionated RBC containing SS hemoglobin, and RBC from four other mammalian species. In the case of human RBC obtained from eight normal donors, we obtained mean MCV values (+/- SD) of 83.6 +/- 3.0, 87.5 +/- 3.9, and 76.5 +/- 5.3 fl for unfractionated and top and bottom 10% density fractions, respectively. The value 83.6 is significantly lower than the generally accepted range of 89-91 indicated by electronic analyzers calibrated against spun microhematocrits. The discrepancy of about 7% can account for the difference between mean cell hemoglobin concentration (MCHC) data determined by a calibrated Coulter Counter and corresponding data obtained with paired samples using a cyanmethemoglobin procedure specified in NCCLS Standard H15-A and corrected for trapped plasma.     

Lecithotrophic development and metamorphosis in the Indo-West Pacific brittle star Ophiomastix venosa (Echinodermata: Ophiuroidea)

Summary

The larval development of the ophiocomid ophiuroid Ophiomastix venosais described using SEM. The gastrula transforms into a uniformly ciliated early larva which progressively changes into a lecithotrophic late premetamorphic larva with a continuous bilateral ciliated band. This stage is short-lived and equivalent to a highly reduced ophiopluteus. Comparisons between O. venosa and other ophiuroid species whose development has been investigated suggest that, whatever the developmental mode (lecithotrophic or planktotrophic), a pluteus stage always occurs in ophiuroids with planktonic development. Two metamorphic stages were identified, the late metamorphic larva differing from the early one by the closure of the larval mouth. The appearance of the permanent mouth marks the end of the metamorphosis. The postlarva still possesses remnants of larval features. The transformation of the reduced ophiopluteus into a barrel-shaped metamorphic larva with transverse ciliated bands, a vitellaria larva, is followed. The possible occurrence of a unique type of metamorphic larva in non-brooding ophiuroids is discussed. Verification of this, however, needs further SEM investigations on metamorphic larva from species having “regular” planktotrophic development.     

Prenatal screening for hemoglobinopathies. III. Applicability of the health belief model.

A comprehensive prenatal hemoglobinopathy screening program in Rochester, NY, has been described in a preceding paper in this issue of the Journal. A woman identified as a carrier may face three decisions. The first is whether to accept the offer of counseling. The second is whether to have her partner tested. If her partner also tests positive, then the third decision is whether to accept the offer of prenatal diagnosis. This report analyzes factors affecting her decision, with special attention being given to factors invoked by the Health Belief Model. Factors predicting that a patient who we identified as a carrier would come for counseling included the following: patient had no prior knowledge that she is a carrier (P less than .001), a gestational age less than 18 wk (P less than .01), and Caucasian race (P less than .05). For sickle cell trait counselees and beta-thalassamia trait counselees, factors found to predict patient's intent to have partner tested were the following: a greater postcounseling knowledge of the disease (P less than .009), a lesser perceived burden of intervention (P less than .011), and belief that the partner is also a carrier (P less than .008). Also for sickle cell trait counselees and beta-thalassemia trait counselees, factors predicting that the partner actually will be tested were the following: living with the partner (P less than .001), gestational age at identification less than or equal to 18 wk (P less than .001), a lesser perceived burden of intervention (P less than .002), and a greater perceived seriousness of the disease (P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)