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C Lichtenstein

Publications and source records attributed to C Lichtenstein.

16 recordsLinked to original sources
PubMed1996

Integration of multiple repeats of geminiviral DNA into the nuclear genome of tobacco during evolution.

Integration of viral DNA into the host nuclear genome, although not unusual in bacterial and animal systems, has surprisingly not been reported for plants. We have discovered geminvirus-related DNA (GRD) sequences, in the form of distinct sets of multiple direct repeats comprising three related repeat classes, situated in a unique locus in the Nicotiana tabacum (tobacco) nuclear genome. The organization of these sequences is similar or identical in eight different tobacco cultivars we have examined. DNA sequence analysis reveals that each repeat has sequences most resembling those of the New World geminiviral DNA replication origin plus the adjacent AL1 gene, encoding the viral replication protein. We believe these GRD sequences originated quite recently in Nicotiana evolution through integration of geminiviral DNA by some combination of the processes of illegitimate recombination, amplification, deletions, and rearrangements. These events must have occurred in plant tissue that was subsequently able to contribute to meristematic tissue yielding gametes. GRD may have been retained in tobacco by selection or by random fixation in a small evolving population. Although we cannot detect transcription of these sequences, this does not exclude the possibility that they may originally have been expressed.

Amino Acid Sequence↗
PubMed1995

Chromosomal location of endogenous geminivirus-related DNA sequences in Nicotiana tabacum L.

The N. tabacum (tobacco) nuclear genome carries approximately 25 multiple direct repeats of a geminivirus-related DNA (GRD) sequence that probably arose by illegitimate recombination, following geminivirus infection, during Nicotiana evolution. Each GRD repeat carries sequences similar to the geminiviral AL1 gene of the tomato golden mosaic virus (TGMV), encoding a protein required for viral DNA replication, plus the cis-essential replication origin. Using a cloned 14-kb GRD repeat sequence as a probe for fluorescence in situ hybridization (FISH), we identified a unique tobacco chromosome carrying GRD. Translocations between chromosomes of the tobacco S and T genomes were used as physical markers by sequentially hybridizing chromosomes with labelled GRD and total genomic DNA from N. sylvestris (equivalent to the S genome). The 25S, 18S and 5.8S ribosomal gene clusters were detected in double-labelling experiments for use as additional markers to identify the chromosomal location of GRD. GRD occupies one site on a homologous pair of small submetacentrics from the T genome characterized by a lack of either translocated segments from the S genome or ribosomal genes. GRD provides an additional marker for the small chromosomes of the T genome and a useful phylogenetic tool.

Chromosome Mapping↗
PubMed1993

What makes an mRNA anti-sense-itive?

Antisense RNA has been used for some time as a versatile tool for silencing gene expression. There is ample evidence for gene regulation by endogenous antisense transcripts in prokaryotes and increasing insight into the molecular mechanisms underlying such regulation. The introduction of antisense gene constructs into eukaryotes has now become routine but the mechanisms by which gene expression is inhibited are barely understood. In recent years, several examples of endogenous eukaryotic antisense transcripts have been discovered, some of which probably serve regulatory functions. Here we will discuss a model to explain mechanisms of antisense-mediated gene silencing.

Animals↗
PubMed1993

Preservation of functioning human thyroid organoids in the scid mouse: 1. System characterization.

We have characterized a system for preserving reconstituted human thyroid follicles in vivo by transplanting human thyrocytes into mice with severe combined immunodeficiency (scid mice). Human thyroid organoids were constructed from thyroid monolayer cells derived from both normal and abnormal thyroid tissue, and embedded within a basement membrane preparation which was then transferred sc to scid mice. As early as 4 weeks, and as late as 3 months post transplantation, histological examination of human thyroid organoids demonstrated widespread neofollicle formation and colloid accumulation which stained positive for human thyroglobulin (hTg). Although there were no changes in murine serum T4 levels; the transplanted thyroid epithelial cells secreted hTg into the scid mouse circulation (with an average level of 29 micrograms/L). In addition, hTg release was stimulated in vivo by ip administration of recombinant human TSH (0.1-1.0 IU/mouse) achieving greater than 20-fold increases in scid mouse serum hTg levels. In situ immunohistochemistry showed that thyroid organoids derived from patients with Graves' disease retained scattered lymphocytes in peripolesis with the thyroid epithelial cells; those lymphocytes were identified as human T cells of the memory (CD45RO +), rather than naive, type. These data demonstrate that functioning human thyroid organoids establish in scid mice and remain responsive to TSH stimulation. The system offers a unique opportunity to examine human thyroid-lymphocyte interaction within the confines of a predictable animal model.

Animals↗
PubMed1991

Purification and characterisation of the TnsB protein of Tn7: a transposition protein that binds to the ends of Tn7.

Tn7, a large bacterial transposon encodes 5 proteins required for its transposition. We report a rapid and easy purification of one of these proteins, TnsB, from an overexpression strain. This protein was shown to bind to the ends of Tn7, in a bandshift assay, in two distinct stages as a function of protein concentration. DNasel footprinting at each end of Tn7 showed that the TnsB recognition sequence, a set of 22 bp repeats, plus Tn7 termini are protected. Binding of TnsB appeared cooperative but was only observed above a threshold concentration of protein. ATP and Mg2+ had no effect on the pattern of protection, nor did addition of other Tn7-encoded proteins. Hydroxyl radical footprinting, performed at the right end, showed that TnsB binds preferentially to one side of the DNA helix.

Bacterial Proteins↗
PubMed1990

DNA sequence analysis of five genes; tnsA, B, C, D and E, required for Tn7 transposition.

A region of DNA sequence of the bacterial transposon Tn7, which is required for transposition, has been determined. This DNA sequence completes an 8351 base pair (bp) region containing five long open reading frames (ORF's) that correspond to the genetically defined genes, tnsA, B, C, D and E, required for Tn7 transposition. All of the ORF's are oriented in the same direction, ie. inward from the element's right end. The genes are in a very compact arrangement with the presumed initiation codons never more than two bases beyond the preceding termination codon. Domains with similarity to the helix-turn-helix genre of Cro-like, sequence specific DNA binding sites occur within the deduced amino acid (a.a.) sequence of the TnsA, TnsB, TnsD and TnsE proteins. Translation of the tnsC ORF reveals strong homology to a consensus sequence for nucleotide binding sites as well as a region of similarity to a transcriptional activator (MalT). No striking a.a. sequence similarity to other DNA recombinases is observed. The possible roles of these proteins in Tn7 transposition is discussed in light of the analysis presented.

Amino Acid Sequence↗
PubMed1989

Health risks of short-term SO2 exposure to exercising asthmatics.

A method is described for quantifying health risks to asthmatics briefly exposed to elevated levels of SO2. By combining symptomological and physiological measurements, we have developed a dose-response surface that relates both severity and incidence of response to ambient air quality levels. The complete model to assess potentially avoidable risks includes power plant emission data; ambient SO2 background levels; demographic and activity patterns of asthmatics, the identified population at risk; and the dose-response surface. The estimated annual risk to persons experiencing an SO2-induced response due to a nearby power plant is quite small (response rates under 3 percent). Uncertainties due to modeling errors, variations in activity patterns, demographics and physiological response are discussed.

Air Pollutants, Occupational↗
PubMed1984

Nucleotide sequence of the tms genes of the pTiA6NC octopine Ti plasmid: two gene products involved in plant tumorigenesis.

The nucleotide sequence of the tumor morphology locus, tms, from pTiA6NC has been determined. The sequence analysis indicates that each of two polyadenylylated transcripts encoded by this locus contains an open reading frame; the predicted transcript 1 gene product has a molecular size of 83,769 daltons, and the predicted transcript 2 gene product, of 49,588 daltons. The precise start and stop positions of the transcript 2 RNA have been mapped with S1 nuclease. Several insertion mutations have been constructed. One of these localizes the transcript 2 promoter within the 72 base pairs 5' to transcription initiation. Significant homology was observed between the protein encoded by transcript 1 and the adenine binding region of p-hydroxybenzoate hydroxylase from Pseudomonas fluorescens, suggesting that the transcript 1 protein binds adenine either as substrate or cofactor.

Amino Acid Sequence↗
PubMed1984

Nucleotide sequence and transcript mapping of the tmr gene of the pTiA6NC octopine Ti-plasmid: a bacterial gene involved in plant tumorigenesis.

The nucleotide sequence of a tumor morphology gene, tmr, from the Agrobacterium tumefaciens Ti-plasmid, pTiA6NC, and its flanking 5' region was determined by M13 "dideoxy" procedures. The DNA sequence reveals an open reading frame capable of encoding a 240 amino acid protein. We have identified the polyadenylated transcript initiation and termination sits by S1 nuclease mapping. The extent of the sequence required for transcription 5' to the start of transcription has been delimited by two transposon insertions. The first of these maps at -- 121 with respect to transcription initiation and results in the wild-type phenotype, the second insertion maps at about -85 and results in a tmr phenotype.

Arginine↗
PubMed1982

DNA from the A6S/2 crown gall tumor contains scrambled Ti-plasmid sequences near its junctions with plant DNA.

The A6S/2 tumor incited on tobacco by Agrobacterium tumefaciens harboring the octopine-type A6 Ti plasmid contains one insert of Ti-plasmid sequences (the T DNA). This 13 kb insert is derived from a colinear sequence in the Ti plasmid (the T region) and becomes attached to plant DNA in the nucleus of the host cell. We have determined the DNA sequence encompassing the left end of the T region of the A6 Ti plasmid and the corresponding portion of the A6S/2 T DNA. The two sequences are identical for at least 806 bp. To the left of the divergence point, the tumor contains five partially overlapping sequences that are direct or inverted repeats of sequences to the right of the divergence point. The Ti plasmid contains only the right member of each of these repeats. We have also performed heteroduplex studies that indicate that this T DNA has a 520 bp inverted repeat of an internal sequence at the right end near its junction with plant DNA. The repeated sequences near the ends of the T DNA resemble the repeats of adenovirus type 12 sequences found near its junction with host DNA. We discuss data suggesting that the 23 bp to the immediate right of the divergence point of the A6 left junction form a site important in some step in the transfer of T-region DNA from the bacteria to the plant.

Base Sequence↗
PubMed1981

Site-specific properties of Tn7 transposition into the E. coli chromosome.

A study has been made of the insertional properties of transposon Tn7, a 14 kilobase transposable element encoding resistances to trimethoprim, streptomycin and spectinomycin. It has previously been shown that Tn7 transposes at a low frequency and with low specificity into multiple sites in large transmissible plasmids. However, Tn7 transposes with extreme specificity and at high efficiency into the E. coli chromosome. In all cases we have studied, insertion of Tn7 into the chromosome has occurred at a unique site and with a unique orientation. A combination of genetic and biochemical techniques have been used to precisely locate this site on the E. coli chromosome to minute 82 on the linkage map between markers glmS and uncA. To investigate the nature of this highly specific transpositional event, a small region of the E. coli chromosome that includes the unique site, was cloned into the plasmid vector pBR322. Subsequently a lkb restriction fragment, including the Tn7 insertion site, was sub-cloned from this plasmid into the plasmid pACYC184. We show that Tn7 transposes into both these plasmid recombinants with the frequency and specificity characteristic of the E. coli chromosome.

Chromosome Mapping↗