Human leukemic K562 cells: differential effects of 5-azacytidine on DNA methylation of epsilon-, gamma-globin and 7SL RNA genes

5 Azacytidine ribonucleoside (5 Aza CR), greatly enhances erythroid differentiation of the K562(h) cell line, with a sharp increase of embryonic and fetal globin gene expression. This phenomenon is correlated with the undermethylation of gamma-globin but not of epsilon-globin, as the epsilon-globin gene is already extensively undermethylated before 5AzaCR induction. By contrast no variations in both DNA methylation and expression are observed in 7SL RNA genes.     

Statistical-mechanical theory of passive transport through partially sieving or leaky membranes

The basic equations for multicomponent transport through partially sieving or leaky membranes are discussed from a statistical-mechanical viewpoint. They have the same mathematical form as the corresponding equations for open membranes, but differ in a discontinuous way from the equations for semipermeable membranes (since a "leak" in a semipermeable membrane constitutes a discontinuous or singular perturbation). Partially sieving membranes can be made to mimic semipermeable behavior through the introduction of characteristic time scales. They may approximate semipermeable behavior at short times, but always deviate at longer times.     

Expression of p53 gene in B-CLL peripheral lymphocytes.

The p53 tumor suppressor gene expression has been studied in 23 B-CLL cases at different clinical stages. The analysis failed to show a direct correlation with each stage, but the significantly lower frequency of a BglII RFLP in the pathologic population suggests a role of this gene in B-CLL. Northern Blot analysis showed the expression of p53 mRNA in all the B-CLL cases. A protocol for the RT-PCR methods was set up to study a very small amount of materials which should be better used for sequence analysis.     

Immunocytochemical detection of dendritic cell by S-100 protein in the chicken.

Positivity for S-100 protein in paraffin embedded chicken lymphoid tissue was found by using a polyclonal antibody against whole bovine S-100 protein. The S-100 protein-containing cells were observed in the locations which have been reported to contain avian dendritic cells such as the medulla of the bursal follicles, and the germinal centers and T-dependent areas in the spleen, Peyer's patches, caecal tonsil and Harderian gland. Positive cells were also found in the location where ellipsoid associated cell have been described, and between epithelial cells covering the Peyer's patches and the caecal tonsil, as well as between the cells lining the ducts within the Harderian gland. Macrophages were devoid of immunostaining. Our results confirm the location described elsewhere for chicken dendritic cells and indicate that S-100 protein can be considered as a cell marker for the identification of the chicken dendritic cell. Intraepithelial positive cells may be interdigitating dendritic cells in an unusual location (their function being the transport of the antigen from the epithelium to the diffuse lymphoid tissue), or cytotoxic T-lymphocytes which, in mammals, are immunoreactive for S-100 protein.     

Cortisol influence on some typical parameters of protein malnutrition in rats (author's transl)

A daily v.s. dose of cortisol administered to rats, induces certain metabolic modifications, which after using the "pair-fed" system have been proven to be at least partially independent of the ingesta decrease originated by cortisol. Both cortisol treatment and experimental proteic malnutrition, originate a decrease in corporal weight, a lessening of the gamma-globulins plasmatic fraction, and an elimination increase in total nitrogen, protein, creatine and creatinine in urine. Cortisol treatment determines an increase in blood red cells number, as well as an increase in total serum proteins, especially albumin, without provoking a lessening in the beta-globulins fraction, as happens in cases of proteic malnutrition.     

The photoreaction center of Rhodospirillum rubrum mutant strain F24.1

Rhodospirillum rubrum strain F24.1 is a spontaneous revertant of nonphototrophic mutant F24 derived from wild-type strain S1. Strain F24 shows no detectable photochemical activity and contains, at most, traces of the photoreaction center polypeptides. Strain F24.1 has a phototrophic growth rate close to that of the wild-type strain (Picorel, R., del Valle-Tascón, S. and Ramírez, J.M. (1977) Arch. Biophys. Biochem. 181, 665–670) but shows little photochemical activity. Light-induced absorbance changes in the near-infrared, photoinduced EPR signals and ferricyanide-elicited absorbance changes indicate that strain F24.1 has a photoreaction center content of 7–8% as compared to strain S1. Polyacrylamide gel electrophoresis of isolated F24.1 chromatophores shows the photoreaction center polypeptides to be present in amounts compatible with this value. Photoreaction center was prepared from strain F24.1 and showed no detectable difference with that of strain S1. It is concluded that strain F24.1 photosynthesis is due entirely to its residual 7–8% of typical photoreaction center.     

Role of histidine-50, glutamic acid-96, and histidine-137 in the ribonucleolytic mechanism of the ribotoxin alpha-sarcin

alpha-Sarcin is a ribotoxin secreted by the mold Aspergillus giganteus that degrades the ribosomal RNA by acting as a cyclizing ribonuclease. Three residues potentially involved in the mechanism of catalysis--histidine-50, glutamic acid-96, and histidine-137--were changed to glutamine. Three different single mutation variants (H50Q, E96Q, H137Q) as well as a double variant (H50/137Q) and a triple variant (H50/137Q/E96Q) were prepared and isolated to homogeneity. These variants were spectroscopically (circular dichroism, fluorescence emission, and proton nuclear magnetic resonance) characterized. According to these results, the three-dimensional structure of these variants of alpha-sarcin was preserved; only very minor local changes were detected. All the variants were inactive when assayed against either intact ribosomes or poly(A). The effect of pH on the ribonucleolytic activity of alpha-sarcin was evaluated against the ApA dinucleotide. This assay revealed that only the H50Q variant still retained its ability to cleave a phosphodiester bond, but it did so to a lesser extent than did wild-type alpha-sarcin. The results obtained are interpreted in terms of His137 and Glu96 as essential residues for the catalytic activity of alpha-sarcin (His137 as the general acid and Glu96 as the general base) and His50 stabilizing the transition state of the reaction catalyzed by alpha-sarcin.     

Preferred proline puckerings in cis andtrans peptide groups: Implications for collagen stability

The interplay between side-chain and main-chain conformations is a distinctive characteristic of proline residues. Here we report the results of a statistical analysis of proline conformations using a large protein database. In particular, we found that proline residues with the preceding peptide bond in the cis state preferentially adopt a down puckering. Indeed, out of 178 cis proline residues, as many as 145 (81%) are down. By analyzing the 1-4 and 1-5 nonbonding distances between backbone atoms, we provide a structural explanation for the observed trend. The observed correlation between proline puckering and peptide bond conformation suggests a new mechanism to explain the reported shift of the cis-trans equilibrium in proline derivatives. The implications of these results for the current models of collagen stability are also discussed.