Nuclear localization of the PEP protein tyrosine phosphatase.

PEP is an intracellular protein tyrosine phosphatase expressed primarily by cells of hematopoietic origin that can be divided structurally into a catalytic domain and a large carboxy-terminal domain. The carboxy-terminal domain is enriched in proline, glutamic acid, serine, and threonine residues (PEST sequences) and contains a nonperfect tandem repeat sequence enriched in proline residues and a carboxy terminus enriched in basic amino acids. Here we show that PEP is diffusely expressed in lymphoid tissues, consistent with expression by many different cell types. Analysis of the PEP protein identifies a nuclear localization sequence within the extreme carboxy terminus. Transfer of 18 amino acids from the carboxy terminus of PEP to beta-galactosidase conferred nuclear localization, indicating that this sequence was sufficient for nuclear localization. Proteins enriched in PEST sequences are often rapidly degraded. However, pulse-chase analysis indicates that PEP has a half-life of greater than 5 h.     

Human autologous rosettes. I. Mechanism of binding of autologous erythrocytes by T cells.

A population of human peripheral blood lymphocytes is able to bind autologous erythrocytes in the presence of autologous serum. Erythrocyte binding is found to be more efficient at 4 °C after preincubation of lymphocytes in autologous serum for 30 min followed by overnight incubation. The overall cellular concentration and erythrocyte/lymphocyte ratio are also crucial in determining the weak erythrocyte binding to autologous lymphocytes. Membrane proteins are involved since the binding structures are sensitive to protease treatment. The 26% RFC obtained with an optimized assay are related to the T-cell lineage.     

Confertdiolide,a novel sesquiterpenoid lactone from Parthenium

Four sesquiterpene lactones were isolated from several populations of Parthenium confertum var. lyratum (Gray) collected in Sierra de Arteaga, southern Coahuila. Three of the compounds, hysterin, tetraneurin E and hymenin were previously isolated from other Parthenium species. The fourth constituent is the new cyclopropanoid sesquiterpene dilactone confertdiolide which represents a new structural type. The photolytic conversion of hymenin into confertdiolide confirmed its structure.     

Use of antibiotics to determine ribosome-messenger RNA interactions necessary for in vivo stability of specific messengers

With the use of inhibitors of individual reactions in protein synthesis, a method has been developed for (a) determining the role of ribosome messenger RNA interactions in specific bacteriophage T4 mRNA stability and (b) localizing the primary site of interaction of messenger ribonuclease (mRNase) on messengers. Antibiotics that freeze ribosomes in or near the initiation site stabilize T4 deoxynucleotide kinase mRNA. In contrast, T4 α-glucosyltransferase mRNA is stable only when the polysome configuration is kept intact. These results indicate the deoxynucleotide kinase mRNA initiation site is most susceptible to mRNase action, whereas the primary site of mRNase action on the α-glucosyltransferase mRNA is distal to the initiation site. Determining the role of ribosome-mRNA interactions in mRNA stability by the use of specific inhibitors of protein synthesis may be applicable to any procaryotic or eucaryotic mRNA that can be translated in vitro.     

Hyposmotic fluid formation in Hydra

A detailed model for hyposmotic fluid formation in Hydra is presented. We propose that enteron fluid formation occurs in two steps: (1) segregation of an isosmotic fluid in large intercellular vacuoles with (2) subsequent reabsorption of solute in the intercellular channels to form the hyposmotic fluid of the enteron. Intercellular spaces in Hydra have been studied by light microscopy and thin-section electron microscopy, as well as by electrophysiological methods. These spaces are of two types: (1) large vacuoles which are located in the cells of both the epidermis and gastrodermis, being more numerous in the epidermis; and (2) lateral intercellular channels which run from the intercellular vacuoles, leading eventually to the enteron. These vacuoles and channels are highly convoluted, forming a complex three-dimensional network. We suggest that this network is involved in the water balance of Hydra.