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G P Nolan

Publications and source records attributed to G P Nolan.

At least 19 recordsLinked to original sources
PubMed1992

The NF-kappa B p50 precursor, p105, contains an internal I kappa B-like inhibitor that preferentially inhibits p50.

The p50 subunit of NF-kappa B is apparently synthesized as a precursor molecule of 105 kDa (p105); subsequent processing releases the amino-terminal p50 polypeptide with rel homology, DNA binding activity and transcriptional activation potential. The carboxy-terminal region of p105 contains seven copies of an ankyrin-related sequence previously found in several genes involved in differentiation and cell cycle control. Two proteins with I kappa B activity, MAD-3 and pp40, have been cloned and found to contain five obvious ankyrin repeats that align with those in the carboxy-terminus of p105. Both proteins target their inhibitory activity to the p65 subunit of NF-kappa B and to c-rel. Here we show that the bacterially expressed and purified carboxy-terminal region (CTR) of p105 abolishes the binding of p50 homodimers to a kappa B motif but minimally affects the binding of p65 homodimers and NF-kappa B. By contrast, MAD-3 inhibits the binding of p65 and NF-kappa B but not p50. Both the CTR and MAD-3 interact with their respective targets through physical association both in vitro and in vivo. The CTR can be expressed as an independent entity and thus may play two roles, as a cis inhibitor built into the p105 molecule and as a trans regulator of p50.

Amino Acid Sequence↗
PubMed1992

The inhibitory ankyrin and activator Rel proteins.

The gene families encoding the proteins NF-kappa B, c-Rel and Dorsal, in conjunction with their respective inhibitors l kappa B, pp40, and Cactus, achieve specificity in gene regulation by means of common principles. The related activities of NF-kappa B and Dorsal are mediated by heterodimeric or homodimeric complexes of proteins containing the conserved dimerization and DNA-binding domain termed Rel. The l kappa Bs and Cactus, which share a core series of structural repeats termed ankyrin, inhibit cognate activators through differential interactions with the Rel-homology domain. Together, the inhibitory ankyrin proteins and their cognate Rel dimers probably define specific signalling pathways able to activate specific gene expression. Both gene families include proto-oncogenes, thus broadly implicating Rel/l kappa B in the control of both normal gene expression and the aberrant gene expression that makes cells cancerous.

Amino Acid Sequence↗
PubMed1992

Independent modes of transcriptional activation by the p50 and p65 subunits of NF-kappa B.

Recombinant subunits of the transcription factor NF-kappa B, p50 and p65, were analyzed both for binding to various kappa B motifs and in vitro activation. The subunits preferentially form a heterodimer that activates transcription. Although p50 and p65 bind DNA individually as homodimers and are structurally related, their activation mechanisms are distinct. p65 activates transcription by its unique carboxy-terminal activation domain. (p50)2 displays higher affinity DNA binding than (p65)2 for many distinct kappa B motifs and provides strong transcriptional activation only when adopting a chymotrypsin-resistant conformation induced by certain kappa B motifs but not others. Thus, (p50)2 acts as a positive regulator in vitro, consistent with its isolation as a putative constitutive regulator of MHC class I genes. Both subunits of NF-kappa B, therefore, contribute independently to provide regulation at given kappa B motifs.

Base Sequence↗
PubMed1991

DNA binding and I kappa B inhibition of the cloned p65 subunit of NF-kappa B, a rel-related polypeptide.

The sequence and biochemical properties of the product of the cloned cDNA for the p65 subunit of nuclear factor kappa B (NF-kappa B) have been determined. The cDNA has an open reading frame of 549 amino acids capable of encoding a 60 kd protein. NF-kappa B p65 contains an amino-terminal region of 320 amino acids with extensive similarity to the oncogene c-rel and lesser similarity to NF-kappa B p50. In vitro translated p65 forms a DNA-binding complex with NF-kappa B p50, and the binding of this complex can be specifically inhibited by purified I kappa B. Progressive carboxy-terminal deletions of p65 show that, contrary to previous assumptions, p65 does include a DNA-binding domain that in vivo might become activated only through hetero-oligomerization with p50. DNA binding by truncated p65 is inhibited by I kappa B, thus mapping the I kappa B interaction domain to the rel-homologous region and suggesting that I kappa B exerts its inhibitory effect upon NF-kappa B primarily through interaction with p65.

Amino Acid Sequence↗
PubMed1991

Whole animal cell sorting of Drosophila embryos.

Use of primary culture cells has been limited by the inability to purify most types of cells, particularly cells from early developmental stages. In whole animal cell sorting (WACS), live cells derived from animals harboring a lacZ transgene are purified according to their level of beta-galactosidase expression with a fluorogenic beta-galactosidase substrate and fluorescence-activated cell sorting. With WACS, incipient posterior compartment cells that express the engrailed gene were purified from early Drosophila embryos. Neuronal precursor cells were also purified, and they differentiated into neurons with high efficiency in culture. Because there are many lacZ strains, it may be possible to purify most types of Drosophila cells. The same approach is also applicable to other organisms for which germ-line transformation is possible.

Animals↗
PubMed1991

Improved FACS-Gal: flow cytometric analysis and sorting of viable eukaryotic cells expressing reporter gene constructs.

The previously reported FACS-Gal assay (Nolan et al., Proc Natl Acad Sci USA 85:2603-2607, 1988) measures E. coli lacZ-encoded beta-galactosidase activity in individual viable eukaryotic cells for a variety of molecular and cellular biological applications. Enzyme activity is measured by flow cytometry, using a fluorogenic substrate, which is hydrolyzed and retained intracellularly. In this system, lacZ serves both as a reporter gene to quantitate gene expression and as a selectable marker for the fluorescence-activated sorting of cells based on their lacZ expression level. This report details the following improvements of the original assay: 1) use of phenylethyl-beta-D-thiogalactoside, a competitive inhibitor, to inhibit beta-galactosidase activity; 2) reduction of false positives by two-color measurements; and 3) inhibition of interfering mammalian beta-galactosidases by the weak base chloroquine. We found an exponential relationship between fluorescence generated by beta-galactosidase in this assay and the intracellular concentration of beta-galactosidase molecules. Finally, we report conditions for optimal loading of the substrate (FDG) and retention of the product, fluorescein. Under these conditions, we found uniform loading of FDG in all cells of a clone in individual experiments. Together, these improvements make FACS-Gal an extremely powerful tool for investigation of gene expression in eukaryotic cells.

Animals↗
PubMed1991

In situ detection of stage-specific genes and enhancers in B cell differentiation via gene-search retroviruses.

We demonstrate that infection of an LPS-responsive pre-B cell line with transcriptionally-defective retroviruses containing a reporter gene (lacZ) can result in viral integrations where expression of lacZ is differentiation stage-dependent. Because expression of lacZ is dependent upon flanking cellular sequences these retroviral integrations represent in situ gene fusions with cellular enhancers (Enhsr1) and genes (Gensr1) which are either induced or repressed during LPS-stimulated differentiation. One of the well-documented effects of LPS upon pre-B cells is the induction of kappa light chain transcription via NF-kappa B. The identification of LPS-stimulated gene repression during B cell differentiation indicates that LPS has multiple effects upon gene expression during the pre-B to B cell transition. The identification of cellular enhancers and genes which are downregulated during the transition from the pre-B to the B cell stage indicates that other transcription factors, in addition to NF-kappa B, are required for this step in differentiation. Finally, we present some initial experiments which indicate the gene-search retroviruses can introduce expression of lacZ into normal hematopoietic cells in vitro and in vivo.

Animals↗
PubMed1991

Effect of N-acetyl-D-glucosamine on the migration of Brugia pahangi microfilariae into the haemocoel of Aedes aegypti.

Two strains of Aedes aegypti (L.), differing in their susceptibility to Brugia pahangi (Buckley & Edeson), were examined with regard to the effect on the proportion of microfilariae migrating from the mid-gut, of specific carbohydrate supplements in the infecting bloodmeal. N-Acetyl-D-glucosamine (GlcNAc), a sugar also present on the microfilarial sheath, significantly increased the migration rate. This enhancement is greater for the refractory strain of Ae.aegypti. The use of sucrose as a control sugar results in no enhancement of microfilariae migration. It is postulated that the GlcNAc is acting by blocking endogenous gut/peritrophic membrane carbohydrate binding proteins, which would normally inhibit microfilariae migration. Furthermore, there is a significant correlation whereby increasing loads of microfilariae ingested result in decreasing proportions migrating across the mid-gut.

Acetylglucosamine↗
PubMed1990

Cloning of the p50 DNA binding subunit of NF-kappa B: homology to rel and dorsal.

The DNA binding subunit of the transcription factor NF-kappa B, p50, has been cloned. p50 appears to be synthesized as a larger protein that is then processed to its functional size. Sequence analysis reveals remarkable homology for over 300 amino acids at the amino-terminal end to the oncogene v-rel, its cellular homolog c-rel, and the Drosophila maternal effect gene dorsal. This establishes NF-kappa B as a member of the rel family of proteins, all of which display nuclear-cytosolic translocation. Protein sequence from the p65 polypeptide has established that it is not encoded in the same mRNA as p50. However, p65 appears homologous to c-rel, suggesting that c-rel may form heterodimers with p50 and rel may include a homodimerization motif.

Amino Acid Sequence↗
PubMed1990

Single cell assay of a transcription factor reveals a threshold in transcription activated by signals emanating from the T-cell antigen receptor.

Stimulation of T lymphocytes through their antigen receptor leads to the appearance of several transcription factors, including NF-AT and NF-kappa B, which are involved in regulating genes required for immunologic activation. To investigate the activity of a single transcription factor in individual viable cells, we have applied an assay that uses the fluorescence-activated cell sorter to quantitate beta-galactosidase (beta-gal). We have analyzed the distribution of NF-AT transcriptional activity among T cells undergoing activation by using a construct in which three tandem copies of the NF-AT-binding site directs transcription of the lacZ gene. Unexpectedly, stimulation of cloned stably transfected Jurkat T cells leads to a bimodal pattern of beta-gal expression in which some cells express no beta-gal and others express high levels. This expression pattern cannot be accounted for by cell-cycle position or heritable variation. Further results, in which beta-gal activity is correlated with NF-AT-binding activity, indicate that the concentration of NF-AT must exceed a critical threshold before transcription initiates. This threshold likely reflects the NF-AT concentration-dependent assembly of transcription complexes at the promoter. Similar constructs controlled by NF-kappa B or the entire interleukin-2 enhancer show bimodal expression patterns during induction, suggesting that thresholds set by the concentration of transcription factors may be a common property of inducible genes.

Cell Cycle↗
PubMed1990

A novel fluorescence-based system for assaying and separating live cells according to VDJ recombinase activity.

We describe two retroviral vector-based recombination substrate systems designed to assay for lymphoid VDJ recombinase activity in cultured cells. Both substrates incorporate a constitutive dominant marker gene (the simian virus promoter-driven neo gene) to allow selection of cells that stably integrate the substrate. Both substrates also include a second marker gene that becomes transcriptionally active only when inverted by a site-specific recombination event between flanking immunoglobulin variable-region gene segments. The first vector, similar in structure to previous retrovirus-based recombination substrates, utilizes the bacterial guanine-xanthine phosphoribosyltransferase gene (gpt) as its activatable marker; detection of inversion (VDJ recombinase activity) involves drug selection and Southern blotting analyses. We have used this vector to make a more extensive and quantitative survey of VDJ recombinase activity in B-lineage cell lines than has previously been performed with stable substrates, and we have compared our results with those of other studies that use transient recombination substrates. In the second vector, the activatable gene is the bacterial beta-galactosidase gene (lacZ). Detection for inversional activation of this gene is achieved by a fluorogenic assay, termed FACS-Gal, that detects beta-galactosidase activity in viable cells. The latter assay has the unique advantage of rapidly detecting cells that undergo recombination and also allows viable sorting of cells on the basis of the presence or absence of VDJ recombinase activity. We have used the lacZ vector to rapidly quantitate VDJ recombinase activity in B-lineage cell lines and compared the results with those obtained with the gpt vector. We have also used the lacZ vector to isolate variant pre-B-cell lines with low and high levels of VDJ recombinase activity.

Animals↗
PubMed1989

In situ detection of transcriptionally active chromatin and genetic regulatory elements in individual viable mammalian cells.

Using a newly developed FACS method for quantifying the expression of the Escherischia coli lacZ reporter gene in viable mammalian cells, we have obtained cloned cell lines in which the expression of lacZ is under the control of native endogenous transcription elements. We infected the murine pre-B cell 70Z/3 with transcriptionally disabled retroviruses containing lacZ and employed the FACS-FDG technique to detect and sort rare lacZ+ cells in which we expect integration is near such endogenous transcription elements. After two rounds of enrichment we obtained a population of cells that was 80-90% positive for lacZ activity. Clones derived from the lacZ+ pool differ from each other with respect to their overall level of lacZ activity as well as in the pattern of lacZ expression among cells within an individual clone. Treatment of these lacZ+ 70Z/3 clones with lipopolysaccharide (LPS; which is known to stimulate differentiation of 70Z/3 from a pre-B cell to an IgM-expressing B cell) greatly decreased lacZ expression in one clone, 7e17. lacZ expression in this clone was 50-100 times lower within 24 hr of LPS addition and coincided with the acquisition of IgM kappa on the surface of 7e17. This suggests that a transcriptionally active domain of chromatin that harbors the lacZ construct is down-regulated during the transition induced by LPS stimulation.

Animals↗
PubMed1988

Fluorescence-activated cell analysis and sorting of viable mammalian cells based on beta-D-galactosidase activity after transduction of Escherichia coli lacZ.

We demonstrate that individual cells infected with and expressing a recombinant retrovirus carrying the Escherichia coli beta-galactosidase gene (lacZ) can be viably stained, analyzed, sorted, and cloned by fluorescence-activated cell sorting based on the levels of lacZ expressed. To accomplish this we have devised a method to enzymatically generate and maintain fluorescence in live mammalian cells. Accumulation of fluorescent products in cells is linear with time, with a direct correlation of fluorescence to enzymatic activity. This technology for beta-galactosidase detection is more sensitive than other available cytochemical or biochemical methods. We have used this procedure to show that the expression of psi-2-MMuLVSVnlsLacZ in the T-cell lymphoma BW5147 and the B-cell hybridoma SP2/0 is not completely stable and that subclones selected by the fluorescence-activated cell sorter for low lacZ activity demonstrate distinctly lower average expression of LacZ. These findings indicate the utility of beta-galactosidase as a reporter molecule at the single-cell level for studies of gene regulation, including studies of promoter efficacy, enhancer activity, trans-acting factors, and other regulatory elements.

Animals↗
PubMed1987

Isolation and characterization of the gene for the murine T cell differentiation antigen and immunoglobulin-related molecule, Lyt-2.

We present here the sequence of the 5310 base pair Hind III-cleaved genomic DNA segment that includes the gene for the Lyt-2, a murine differentiation antigen expressed on most immature T lymphocytes as well as the cytotoxic suppressor T cell subset. We also present the complete intron/exon structure of Lyt-2. There are five exons: a fused leader and immunoglobulin variable region like exon, a hinge region exon, a transmembrane exon and two alternatively spliced intracytoplasmic exons (alternative splicing of these exons yields the 38 kDa alpha and 34 kDa alpha' Lyt-2 polypeptides). The promotor region contains a "TATA" box and sequences homologous to the putative immunoglobulin transcriptional control elements cd/pd. S1 protection analysis reveals that thymocytes, T cells from lymph nodes, and a Lyt-2 transfectant obtained by introduction of total genomic DNA have the same initiation site. In the 3' region, there is a polyadenylation signal sequence after a 700 bp long 3' untranslated region.

Amino Acid Sequence↗
PubMed1986

Formal proof that different-size Lyt-2 polypeptides arise from differential splicing and post-transcriptional regulation.

We recently isolated the gene and a cDNA clone for the mouse T-cell surface antigen Lyt-2 and showed that Lyt-2 is homologous to the human Leu-2 (T8) antigen and that the gene encoding it is a member of the immunoglobulin gene superfamily. By screening a mouse thymus cDNA library with the Lyt-2 cDNA clone, we isolated two classes of cDNA clones, alpha and alpha', which differ by 31 base pairs. Comparison of the alpha cDNA with genomic sequence data indicates that there are five exons encoding Lyt-2: a fused leader/immunoglobulin variable region-like exon, a spacer region exon, a transmembrane exon, and two cytoplasmic exons. The alpha' cDNA clones lack the first of the two cytoplasmic exons and have a direct splice from the donor splice site of the transmembrane exon to the acceptor of the second cytoplasmic exon. This splice changes the reading frame for the second cytoplasmic exon, causing a stop codon shortly after the splice so that the alpha' cDNA clone codes for a peptide 25 residues shorter than the alpha cDNA-encoded peptide. We have constructed expression vectors with alpha and alpha' cDNAs and have shown that L-cell transfectants of these produce Lyt-2 polypeptides of the predicted sizes and that these associate as homodimers on the cell membranes. We found the two species of mRNA corresponding to alpha and alpha' cDNAs at equal levels in thymus RNA by using S1 nuclease analysis. Although lymph node T cells have only the alpha form of Lyt-2 protein, S1 nuclease analysis shows that lymph nodes have about 20% alpha' mRNA relative to alpha. Thus, Lyt-2 is regulated at RNA processing, translational, and/or post-translational steps.

Animals↗
PubMed1985

Molecular cloning of Lyt-2, a membrane glycoprotein marking a subset of mouse T lymphocytes: molecular homology to its human counterpart, Leu-2/T8, and to immunoglobulin variable regions.

The sequence of Lyt-2 cDNA shows that it is a new member of the immunoglobulin super gene family. Analysis of the predicted amino acid sequence indicates that the Lyt-2 polypeptide is synthesized with a 27-amino acid leader, and that the mature protein has an immunoglobulin variable region (Ig V)-related sequence of approximately 100 amino acids, an extracellular spacer of 43, a transmembrane region of 38, and an intracytoplasmic region of 27 amino acids. Lyt-2 and its human analogue Leu-2 are 56% homologous; analysis indicates that the Ig V-related domains of the two molecules have evolved away from each other faster than the carboxyl-terminal half of the proteins.

Amino Acid Sequence↗
PubMed1984

Molecular weight determination program.

A computer program is described that will determine the molecular weight of DNA, RNA or protein molecules separated according to size by gel electrophoresis. It uses the sizes and migration distances of known molecules in a reference lane to compute a second or third order equation whose curve best fits the data points. It then computes the sizes of all molecules from this equation. Migration distances are measured and entered using an analog tablet. The program is written in Apple Pascal and designed to run on an Apple II Plus computer.

Computers↗