Exclusion of erythrocyte-specific membrane proteins from clathrin- coated pits during differentiation of human erythroleukemic cells

When human erythroleukemic cells are induced to differentiate, they produce globin and redistribute glycophorin and spectrin to one pole of the cell. This process was accompanied by an alteration in the clathrin-coated pits at the cell surface. In nondifferentiating cells, receptors for Concanavalin A have been shown, using electron microscopy, to be concentrated into coated pits and rapidly internalized. Glycophorin was also internalized via coated pits, but was not greatly concentrated into these portions of the surface membrane. Ligands attached to glycophorin were, therefore, cleared from the cell surface more slowly than Concanavalin A. In nondifferentiating cells, immunoelectron microscopy showed that spectrin is largely excluded from coated pits. After erythroid differentiation proceeded for several days, glycophorin was totally excluded from the coated pits along with spectrin. This did not reflect a general cessation of endocytosis, however, because Concanavalin A receptors continued to be internalized. It is possible that the specific exclusion of glycophorin from coated pits is part of the remodeling process that occurs when the precursor cell membrane differentiates into that of the mature erythrocyte.     

High-speed preparative-scale separation and purification of ribosomal 5S and 5.8S RNA's via Sephacryl S-300 gel filtration chromatography

In this work we present a rapid and economical alternative to Sephadex and high performance size exclusion chromatography (HPSEC) for preparative-scale separation and purification of low molecular weight RNA's: 5.8S RNA, 5S RNA, and tRNA's. These three RNA species can be well resolved from each other and from higher molecular weight RNA species via Sephacryl S-300 gel filtration chromatography under mild eluting conditions: 10 mM Tris-HCl buffer, pH 7.5, containing 1.0 M NaCl. For a sample load of about 250 mg, the resolving power of a Sephacryl S-300 column (78 X 3.2 cm) is comparable to that of a 4.5 times larger Sephadex G-75 column (144 X 5 cm). Moreover, the total separation period is 2.5 times shorter for the Sephacryl method. Up to 500 mg or more of crude ribosomal RNA mixtures could be separated via two Sephacryl S-300 columns operated in tandem.     

Multiline varieties and disease control

Summary Existing theoretical models have led to conflicting predictions concerning the likely effect of the widespread use of dirty crop multilines on the evolution of virulence in pathogen populations. Here we attempt to clarify these problems by extending existing models to include selection against unnecessary genes for virulence at two different stages in the life cycle of the pathogen. The results of these studies indicate that the stage of the life cycle at which selection occurs can significantly influence the evolution of virulence in pathogen populations growing on multiline varieties.     

Human alpha- and beta-CGRP and rat alpha-CGRP are coronary vasodilators in the rat

The effects of the recently described human alpha-calcitonin gene-related peptide (CGRP), human beta-CGRP and rat alpha-CGRP have been compared with those of the vasodilator sodium nitroprusside, on the rat and rabbit isolated heart. Hearts were perfused at constant flow and [Arg8]-vasopressin was used to increase coronary perfusion pressure. In the rat heart, the order of potency for evoking cumulative dose-dependent falls in perfusion pressure was human beta-CGRP greater than rat alpha-CGRP greater than human alpha-CGRP greater than sodium nitroprusside. In the same preparations the three CGRPs (but not sodium nitroprusside) elicited cumulative dose-related increases in heart rate. In the rabbit heart the order of potency for vasodilatation was rat alpha-CGRP greater than human alpha-CGRP greater than sodium nitroprusside. In marked contrast to results from the rat, neither rat alpha-CGRP nor human alpha-CGRP altered heart rate in the rabbit isolated heart. These results show that human alpha- and beta-CGRP and rat alpha-CGRP are vasodilators in the coronary vasculature, but that there is species variation as CGRP had a positive chronotropic effect in the rat heart but not in the rabbit heart.     

Malignant transformation of murine fibroblasts by a human c-Ha-ras-1 oncogene does not require a functional epidermal growth factor receptor.

Although mutations in ras genes are thought to be important for the development of about 20% of human tumors, almost nothing is known about the way in which these mutations lead to cellular transformation. The known biochemical properties of the 21-kilodalton ras proteins suggest that they may behave as G proteins, regulating the proliferation of cells in response to growth factor stimulation of a receptor. Although the putative receptor(s) has not been identified, several lines of evidence, in particular the fact that rodent cell lines containing ras oncogenes produce transforming growth factor alpha, have suggested that the epidermal growth factor (EGF) receptor is involved in ras transformation. Here we show that murine fibroblasts with no EGF receptors can be transformed to a completely malignant phenotype with a mutated ras gene. It appears, therefore, that the EGF receptor is not required for ras-mediated transformation of these cells.     

The effect of papain upon proline and sodium transport of rat renal brush-border membrane vesicles

Treatment of renal brush-border membrane vesicles with papain resulted in the removal of the activity of maltase, gamma-glutamyl transpeptidase and leucine aminopeptidase by 85, 50 and 75%, respectively. Stripping of these membrane enzyme activities constituted about 2% of the total membrane proteins and resulted in a widespread diminution in the ability of a variety of amino acids and sugars to be taken up by the membrane vesicles which remained osmotically responsive. Kinetic analysis of the uptake of proline, which was shown previously to be transported by both sodium-dependent and sodium-independent systems, revealed that the Vmax for the sodium-dependent system and Km for the sodium-independent system were halved, but other parameters were not affected indicating that the papain treatment altered sodium-gradient-stimulated entry and the affinity of the sodium-gradient-independent system for proline. Experiments on sodium entry and efflux demonstrate a marked enhancement of flux, so that equilibration of the sodium gradient occurred about 5-times more rapidly than in untreated vesicles. This occurred without any change in the osmotic properties of the vesicle with regard to sodium or amino acid uptake. Studies of fluorescence polarization suggest that incubation with papain does not alter the lipid domains of the membrane.     

Initial Phases of Starvation and Activity of Bacteria at Surfaces

The activity of the hydrophilic Vibrio sp. strain DW1 and the hydrophobic Pseudomonas sp. strain S9, which both undergo starvation-induced responses, was examined at nutrient-enriched and nutrient-deficient interfaces. The initial period of response to a starvation regime (“dwarfing” phase) is a sequence of two processes: fragmentation and continuous size reduction of the fragmented cells. This dwarfing phase is also one of intense metabolic activity as supported by O₂ uptake measurements of the endogenous metabolism and the use of inhibitors of the proton flow, the electron transport chain, and membrane-bound ATPase. Hydrophilic bacteria become even smaller at nutrient-deficient surfaces than in the liquid phase upon starvation, and this is reflected in a higher endogenous metabolism exhibited by surface-associated cells compared with those in the liquid phase. On the other hand, hydrophobic bacteria dwarfing at surfaces did not exhibit a greater size reduction and exhibited an endogenous metabolism that was only slightly higher than that of cells in the liquid phase. Bacterial scavenging of surface-localized nutrients is related to the degree of irreversible binding of dwarf and starved bacteria, which in turn may be related to the degree of cell surface hydrophobicity.     

Determination of base pairing in ribonucleic acid by Fourier-transform infrared spectrometry: yeast ribosomal 5S ribonucleic acid

Fourier-transform infrared (FT-IR) spectra of yeast ribosomal 5S RNA have been acquired at several temperatures between 30 and 90 degrees C. The difference spectrum between 90 (bases unstacked) and 30 degrees C (bases stacked) provides a measure of base stacking in the RNA. Calibration difference spectra corresponding to stacking of G-C or A-U pairs are obtained from "reference" FT-IR spectra of poly(rG) X poly(rC) minus 5'-GMP and 5'-CMP or poly(rA) X poly(rU) minus 5'-AMP and 5'-UMP. The best fit linear combination of the calibration G-C and A-U difference spectra to the 5S RNA (90-30 degrees C) difference spectrum leads to a total of 25 +/- 3 base pairs (17 G-C pairs + 8 A-U pairs) for the native yeast 5S RNA in the absence of Mg2+. In the presence of Mg2+, an additional six base pairs are detected by FT-IR (one G-C and five A-U). FT-IR melting curve midpoints show that A-U and G-C pairs melt together (65 and 63 degrees C) in the presence of Mg2+ but A-U pairs melt before G-C pairs (47 vs. 54 degrees C) in the absence of Mg2+.