Physical properties and gel electrophoresis behavior of R12-derived plasmid DNAs.

A series of closed circular (I) plasmid DNAs has been derived from drug resistance factor R12, and the nicked circular (II) and linear (III) derivatives of these molecules prepared by irradiation in the presence of ethidium bromide and by treatment with restriction enzyme EcoRI, respectively. These DNAs encompass the molecular weight range 3.6 to 61 megadaltons. The base compositions range from 45% to 51% (GC) as estimated by buoyant density determinations. The smaller plasmids are significantly less supercoiled (9-10%) than are the larger (12-13%). The gel electrophoretic behavior of the three DNA structural forms was determined as a function of molecular weight in agarose gels of concentrations ranging from 0.7% to 1.6% and at electrophoresis salt concentrations from 0.02 M to 0.08 M sodium acetate. The mobilities of DNAs I and III undergo a reversal relative to each other at a molecular weight which decreases with increasing agarose gel concentration. The molecular weight at which DNA II fails to enter a gel depends upon the ionic strength during electrophoresis but not upon the gel concentration.     

Chimpanzee bipedal locomotion in the Gombe National Park,East Africa

An adult male chimpanzee in the natural habitat has been observed to walk predominantly bipedally after a total forelimb paralysis in 1966. The major differences from previously described bipedal chimpanzee gait are (1) one third of the femoral extension is posterior to the hip joint in propulsion, (2) excursion of the swinging foot is close to midline, due to adduction of the lower hindlimb in swing and propulsive phases, (3) depressed pelvic tilt is on the side of the swinging limb, (4) thoracic vertebrae rotate and are vertical and erect, and (5) there is only a moderate lateral sway of the midline. This locomotory complex is interpreted as individual variability and suggests an evolutionary model for the origin of hominid bipedal locomotion.     

Net charge and oxygen affinity of human hemoglobin are independent of hemoglobin concentration

The dependence of net charge and oxygen affinity of human hemoglobin upon hemoglobin concentration was reinvestigated. In contrast to earlier reports from various laboratories, both functional properties of hemoglobin were found to be independent of hemoglobin concentration. Two findings indicate a concentration-independent net charge of carbonmonoxy hemoglobin at pH 6.6: (A) The pH value of a given carbonmonoty hemoglobin solution remains constant at 6.6 when the hemoglobin concentration is raised from 10 to 40 g/dl, indicating that there is no change in protonation of titratable groups of hemoglobin: (b) the net charge of carbonmonoxy hemoglobin as estimated from the Donnan distribution of 22Na+ shows no dependence on hemoglobin concentration in this concentration range. The oxygen affinity of human hemoglobin was determined from measurements of oxygen concentrations in equilibrated samples using a Lex-O2-Con apparatus (Lexington Instruments, Waltham, Mass.). P50 averaged 11.4 mm Hg at 37 degrees C, pH = 7.2, and ionic strength approximately 0.15. Neither P50 nor Hill's n showed any variation with hemoglobin concentrations increasing from 10 to 40 g/dl.     

The human lambda L chain Ig locus. Recharacterization of JC lambda 6 and identification of a functional JC lambda 7

The human lambda L chain Ig gene complex consists of multiple JC gene segments. A seventh human lambda C region gene segment, C lambda 7, was found 2.7 kb downstream of C lambda 6 in this gene complex. A J lambda gene segment, J lambda 7, was found 1.2 kb upstream of C lambda 7 and contains potentially functional nonamer and heptamer recombination sites, an RNA splice site and J coding region. C lambda 7 maintains an open reading frame and encodes a new lambda isotype. C lambda 7 encodes Kern+ and Oz- determinants, but does not encode any of the Kern+Oz- myeloma proteins published to date. Nevertheless, we present evidence that JC lambda 7 is transcribed in normal lymphocytes and is functional. In contrast, we present new data that the C lambda 6 gene segment, reported by others to encode the Kern+Oz- protein, is non-functional due to a 4-bp insertion in our cosmid clone. The 4-bp insertion was characterized further in 32 genomic DNA samples by producing a distinctive restriction fragment length and verified by the DNA sequences of the polymerase chain reaction products of two different cell lines. We discuss the possibility that the Kern+Oz- myeloma proteins do not define an isotype and are not encoded by JC lambda 7 nor other non-allelic genes, and we discuss the level of expression of JC lamba 7 as compared to that of JC lambda 2 and JC lambda 3.     

Changes in cell nuclei during S phase: progressive chromatin condensation and altered expression of the proliferation-associated nuclear proteins Ki-67, cyclin (PCNA), p105, and p34.

Using multiparameter flow cytometry we have measured the nuclear DNA content of exponentially growing HL-60 cells in conjunction with protein content, nuclear forward light scatter, DNA in situ sensitivity to denaturation, DNA accessibility to 7-aminoactinomycin D (7-AMD), and content of the proliferation-associated proteins: cyclin (PCNA), p105, p34, and Ki-67. Multivariate analysis of the data made it possible to correlate changes in each parameter with the degree of cell advancement through S phase (amount of replicated DNA). A decrease of the protein/DNA ratio, lowered DNA accessibility to 7-AMD, increased sensitivity of DNA to denaturation, and increased ability of isolated nuclei to scatter light all paralleled cell progression through S phase. These changes indicate that during S phase chromatin progressively condenses and suggest that the condensation is associated with the efflux of nonhistone proteins from the nucleus. The increase in the content of the antigen detected by the Ki-67 antibody was observed to exceed the increase in DNA content during S phase and the rate of the Ki-67/DNA increase was higher during the second half of S phase. Thus, this protein appears to be primarily synthesized during S, especially late in S phase, and is degraded in G1. The ratio of cyclin (PCNA)/DNA remained rather constant whereas the contents of p105 and p34 proteins, when expressed per unit of DNA, both decreased during S phase. The data indicate that significant changes in structure and composition of chromatin take place during S phase and suggest that the composition of chromatin associated with the nonreplicated DNA is different compared to chromatin associated with the newly replicated DNA.     

Identification and differential expression of a novel alternative splice isoform of the beta A4 amyloid precursor protein (APP) mRNA in leukocytes and brain microglial cells.

The gene for the beta A4-amyloid precursor protein (APP) consists of 19 exons which code for a typical N- and O-glycosylated transmembrane protein with four extracellular domains followed by the transmembrane domain and a short cytoplasmic domain. The beta A4-amyloid sequence is part of exons 16 and 17. Several APP isoforms can be generated by alternative splicing of exons 7 and 8, encoding domains with homologies to Kunitz-type protease inhibitors and the MRC OX-2 antigen, respectively. The mechanism by which the pathological beta A4 is generated is unknown, it is however a critical event in Alzheimer's disease and is distinct from the normally occurring cleavage and secretion of APPs within the beta A4 sequence. We report here for the first time considerable APP mRNA expression by rat brain microglial cells. In addition we showed by S1 nuclease protection and polymerase chain reaction analysis of reverse transcribed RNA (RT-PCR) that T-lymphocytes, macrophages, and microglial cells expressed a new APP isoform by selection of a novel alternative splice site and exclusion of exon 15 of the APP gene. This leads to a transmembrane, beta A4 sequence containing APP variant, lacking 18 amino acid residues close to the amyloidogenic region. The use of this novel alternative splice site alters the structure of APP in close proximity to the beta A4 region and thus may determine a variant, potentially pathogenic processing of leukocyte-derived APP in brain.     

Molecular characterization of the variable regions of a mouse polyreactive IgG2b antibody with rheumatoid factor activity

The complete nucleotide sequences of heavy and light chains of a mouse polyreactive IgG2b antibody were determined. This antibody, obtained after primary immunization of BALB/c mice with human lymphoblastoid cells, possess anti-HLA-DR and anti-rheumatoid factor activities and reacts with various self and nonself antigens. The VL and VH segments were found to belong to the VK8 and VH7183 families, respectively. The VH segment shared a high percentage of sequence similarity (95%) with previously described germline genes. The VK segment had 98.9% of sequence similarity with a consensus sequence VK8 of antibodies with anti-phosphorylcholine activity. Furthermore, the framework regions 2 and 3 of the VL segment were very similar to the framework regions 2 and 3 of other antibodies known to possess rheumatoid factor activity. We postulate that during immunization, the presence of HLA-DR antigens selects precursors having configurations similar to that of the germline, and induces some somatic mutations that do not significantly affect antibody polyreactivity.The nucleotide sequence data reported in this paper have been submitted to the EMBL nucleotide sequence database and have been assigned the accession numbers X53400 and X59816 for VH and VL respectively.     

Inhibition of HIV-1 IIIb replication in AA-2 and MT-2 cells in culture by two ligands of poly (ADP-ribose) polymerase: 6-amino-1,2-benzopyrone and 5-iodo-6-amino-1,2-benzopyrone

The effects of two adenosine diphosphoribose transferase (ADPRT) enzyme inhibitory ligands, 6-amino-1,2-benzopyrone and its 5-iodo-derivative, were determined in AA-2 and MT-2 cell cultures on the replication of HIV-1 IIIb, assayed by an immunochemical test for the HIV protein p24, and syncytium formation, characteristic of HIV-infected cells. Intracellular concentrations of both drugs were sufficient to inhibit poly(ADP-ribose) polymerase activity within the intact cell. Both drugs inhibited HIV replication parallel to their inhibitory potency on ADPRT, but distinct differences were ascertained between the two cell lines. In AA-2 cells both p24 and syncytium formation were depressed simultaneously, whereas in MT-2 cells only syncytium formation was inhibited by the drugs, and the p24 production, which remained unchanged during viral growth, was unaffected. Both drugs only moderately depressed the growth rate of the AA-2 and MT-2 cells and there was no detectable cellular toxicity. Results suggest the feasibility of the development of a new line of ADPRT ligand anti-HIV drugs that fundamentally differ in their mode of action from currently used chemotherapeutics.     

Half-life of the Rous sarcoma virus transforming protein pp60src and its associated kinase activity.

The half-life of metabolically labeled pp60src of the Prague A strain of Rous sarcoma virus and of several transformation-defective, temperature-sensitive mutants was investigated by pulse-labeling infected cells with [35S]methionine, chasing for different times, and immunoprecipitating pp60src with tumor-bearing rabbit serum. These experiments showed that pp60src has a short half-life of approximately 60 min under normal physiological conditions and that the mutant pp60src proteins have similar half-lives to the wild type, irrespective of whether the cells are kept at the nonpermissive (42 degrees C) or permissive (35 degrees C) temperature. The half-life of the pp60src -associated kinase activity was determined by monitoring its decay by the immunoglobulin G heavy chain assay after the cells had been treated with several inhibitors of protein synthesis. In these experiments the kinase half-life was much longer than expected from the half-life of pp60src. The apparent contradiction between the half-lives of the kinase activity and the [35S]methionine-labeled pp60src protein could be resolved by the observation that treatment of cells with inhibitors of protein synthesis stabilized pp60src, resulting in a greatly extended half-life. Inhibitors of protein synthesis also extended the half-life of the gag precursor polypeptide, Pr76, suggesting that a host factor(s) may be required for the efficient intracellular processing of this polypeptide to the gag proteins.