Transduction of nondividing cells using pseudotyped defective high-titer HIV type 1 particles

The use of Moloney murine leukemia virus (Mo-MLV)-based vectors to deliver therapeutic genes into target cells is limited by their inability to transduce nondividing cells. To test the capacity of HIV-based vectors to deliver genes into nondividing cells, we have generated replication-defective HIV type 1 (HIV-1) reporter vectors carrying neomycin phosphotransferase or mouse heat stable antigen, replacing the HIV-1 sequences encoding gp160. These vectors also harbor inactive vpr, vpu, and nef coding regions. Pseudotyped HIV-1 particles carrying either the ecotropic or the amphotropic Mo-MLV envelope proteins or the vesicular stomatitis virus G protein were released after single or double transfections of either human 293T or monkey COS-7 cells with titers of up to 107 colony-forming units per milliliter. A simple ultrafiltration procedure resulted in an additional 10- to 20-fold concentration of the pseudotyped particles. These vectors along with Mo-MLV-based vectors were used to transduce primary human skin fibroblasts and human peripheral blood CD34+ cells. The HIV-1 vector system was significantly more efficient than its Mo-MLV-based counterpart in transducing human skin fibroblasts arrested at the G0/G1 stage of the cell cycle by density-dependent inhibition of growth. Human CD34+ cells were transduced efficiently using HIV-1 pseudotype particles without prior stimulation with cytokines.

Magnesium-Chelatase from Developing Pea Leaves1 : Characterization of a Soluble Extract from Chloroplasts and Resolution into Three Required Protein Fractions

Mg-chelatase catalyzes the ATP-dependent insertion of Mg2+ into protoporphyrin-IX to form Mg-protoporphyrin-IX. This is the first step unique to chlorophyll synthesis, and it lies at the branch point for porphyrin utilization; the other branch leads to heme. Using the stromal fraction of pea (Pisum sativum L. cv Spring) chloroplasts, we have prepared Mg-chelatase in a highly active (1000 pmol 30 min−1 mg−1) and stable form. The reaction had a lag in the time course, which was overcome by preincubation with ATP. The concentration curves for ATP and Mg2+ were sigmoidal, with apparent Km values for Mg2+ and ATP of 14.3 and 0.35 mm, respectively. The Km for deuteroporphyrin was 8 nm. This Km is 300 times lower than the published porphyrin Km for ferrochelatase. The soluble extract was separated into three fractions by chromatography on blue agarose, followed by size-selective centrifugal ultrafiltration of the column flow-through. All three fractions were required for activity, clearly demonstrating that the plant Mg-chelatase requires at least three protein components. Additionally, only two of the components were required for activation; both were contained in the flow-through from the blue-agarose column.

Purification and characterization of a luminal cholecystokinin-releasing factor from rat intestinal secretion.

Cholecystokinin (CCK) secretion in rats and humans is inhibited by pancreatic proteases and bile acids in the intestine. It has been hypothesized that the inhibition of CCK release caused by pancreatic proteases is due to proteolytic inactivation of a CCK-releasing peptide present in intestinal secretion. To purify the putative luminal CCK-releasing factor (LCRF), intestinal secretions were collected by perfusing a modified Thiry-Vella fistula of jejunum in conscious rats. From these secretions, the peptide was concentrated by ultrafiltration followed by low-pressure reverse-phase chromatography and purified by reverse-phase high-pressure liquid chromatography. Purity was confirmed by high-performance capillary electrophoresis. Fractions were assayed for CCK-releasing activity by their ability to stimulate pancreatic protein secretion when infused into the proximal small intestine of conscious rats. Partially purified fractions strongly stimulated both pancreatic secretion and CCK release while CCK receptor blockade abolished the pancreatic response. Amino acid analysis and mass spectral analysis showed that the purified peptide is composed of 70-75 amino acid residues and has a mass of 8136 Da. Microsequence analysis of LCRF yielded an amino acid sequence for 41 residues as follows: STFWAYQPDGDNDPTDYQKYEHTSSPSQLLAPGDYPCVIEV. When infused intraduodenally, the purified peptide stimulated pancreatic protein and fluid secretion in a dose-related manner in conscious rats and significantly elevated plasma CCK levels. Immunoaffinity chromatography using antisera raised to synthetic LCRF-(1-6) abolished the CCK releasing activity of intestinal secretions. These studies demonstrate, to our knowledge, the first chemical characterization of a luminally secreted enteric peptide functioning as an intraluminal regulator of intestinal hormone release.

Promotion of purine nucleotide binding to thymidylate synthase by a potent folate analogue inhibitor, 1843U89.

A folate analogue, 1843U89 (U89), with potential as a chemotherapeutic agent due to its potent and specific inhibition of thymidylate synthase (TS; EC 2.1.1.45), greatly enhances not only the binding of 5-fluoro-2'-deoxyuridine 5'-monophosphate (FdUMP) and dUMP to Escherichia coli TS but also that of dGMP, GMP, dIMP, and IMP. Guanine nucleotide binding was first detected by CD analysis, which revealed a unique spectrum for the TS-dGMP-U89 ternary complex. The quantitative binding of dGMP relative to GMP, FdUMP, and dUMP was determined in the presence and absence of U89 by ultrafiltration analysis, which revealed that although the binding of GMP and dGMP could not be detected in the absence of U89 both were bound in its presence. The Kd for dGMP was about the same as that for dUMP and FdUMP, with binding of the latter two nucleotides being increased by two orders of magnitude by U89. An explanation for the binding of dGMP was provided by x-ray diffraction studies that revealed an extensive stacking interaction between the guanine of dGMP and the benzoquinazoline ring of U89 and hydrogen bonds similar to those involved in dUMP binding. In addition, binding energy was provided through a water molecule that formed hydrogen bonds to both N7 of dGMP and the hydroxyl of Tyr-94. Accommodation of the larger dGMP molecule was accomplished through a distortion of the active site and a shift of the deoxyribose moiety to a new position. These rearrangements also enabled the binding of GMP to occur by creating a pocket for the ribose 2' hydroxyl group, overcoming the normal TS discrimination against nucleotides containing the 2' hydroxyl.