Biomedical subjects

C S Waddell

Publications and source records attributed to C S Waddell.

10 recordsLinked to original sources

PubMed2000

FARE, a new family of foldback transposons in Arabidopsis.

A new family of transposons, FARE, has been identified in Arabidopsis. The structure of these elements is typical of foldback transposons, a distinct subset of mobile DNA elements found in both plants and animals. The ends of FARE elements are long, conserved inverted repeat sequences typically 550 bp in length. These inverted repeats are modular in organization and are predicted to confer extensive secondary structure to the elements. FARE elements are present in high copy number, are heterogeneous in size, and can be divided into two subgroups. FARE1's average 1.1 kb in length and are composed entirely of the long inverted repeats. FARE2's are larger, up to 16.7 kb in length, and contain a large internal region in addition to the inverted repeat ends. The internal region is predicted to encode three proteins, one of which bears homology to a known transposase. FARE1.1 was isolated as an insertion polymorphism between the ecotypes Columbia and Nossen. This, coupled with the presence of 9-bp target-site duplications, strongly suggests that FARE elements have transposed recently. The termini of FARE elements and other foldback transposons are imperfect palindromic sequences, a unique organization that further distinguishes these elements from other mobile DNAs.

Amino Acid Sequence↗

PubMed2000

The rib1 mutant is resistant to indole-3-butyric acid, an endogenous auxin in Arabidopsis.

The presence of indole-3-butyric acid (IBA) as an endogenous auxin in Arabidopsis has been recently demonstrated. However, the in vivo role of IBA remains to be elucidated. We present the characterization of a semi-dominant mutant that is affected in its response to IBA, but shows a wild-type response to indole-3-acetic acid (IAA), the predominant and most studied form of auxin. We have named this mutant rib1 for resistant to IBA. Root elongation assays show that rib1 is specifically resistant to IBA, to the synthetic auxin 2,4-dichlorophenoxyacetic acid, and to auxin transport inhibitors. rib1 does not display increased resistance to IAA, to the synthetic auxin naphthalene acetic acid, or to other classes of plant hormones. rib1 individuals also have other root specific phenotypes including a shortened primary root, an increased number of lateral roots, and a more variable response than wild type to a change in gravitational vector. Adult rib1 plants are morphologically indistinguishable from wild-type plants. These phenotypes suggest that rib1 alters IBA activity in the root, thereby affecting root development and response to environmental stimuli. We propose models in which RIB1 has a function in either IBA transport or response. Our experiments also suggest that IBA does not use the same mechanism to exit cells as does IAA and we propose a model for IBA transport.

2,4-Dichlorophenoxyacetic Acid↗

PubMed1993

High-frequency germinal transposition of DsALS in Arabidopsis.

We have established an efficient transposontagging system in Arabidopsis thaliana using the Activator/Dissociation (Ac/Ds) elements from maize. This system consists of two components, a stable trans-activator, Acst, that supplies transposase, and a cis-responsive Ds element. Ds and Acst were constructed with different selectable and screenable markers to facilitate monitoring of Ds excisions and insertions as well as segregation of Ds and Acst. Fusions of the 35S, rbcS, or CHS promoters to Ac transposase were used to trans-activate DsALS, a Ds element carrying an herbicide-resistance gene. The ALS gene encoding acetolactase synthase, which confers resistance to chlorsulfuron, functioned as a versatile marker for selection of plants grown in tissue culture as well as in soil. Thirty-five Acst lines were crossed to two DsALS lines, and the resulting progeny were assayed for germinal transposition of DsALS. Trans-activation of DsALS by Acst resulted in germinal excision frequencies of up to 64% when using 35S promoter-Ac transposase fusions, up to 67% when using rbcS-transposase fusions, and up to 1% when using CHS-transposase fusions. Amongst progeny bearing terminal excisions, Southern analysis revealed that 45% from 35S-Acst crosses and 29% from rbcS-Acst crosses carried reintegrated DsALS elements. The Ac/Ds system we have developed should prove to be an effective tool for stable gene tagging in Arabidopsis.

Arabidopsis↗

PubMed1989

Tn7 transposition: recognition of the attTn7 target sequence.

The bacterial transposon Tn7 encodes two distinct but overlapping transposition pathways. tnsABC + tnsD promote transposition to a specific site, attTn7, while tnsABC + tnsE promote transposition to many other sites unrelated to attTn7. We have identified a tnsD-dependent DNA binding activity that specifically recognizes attTn7. We have localized the recognition sequences for this activity to a 28-base-pair region and have shown that this same region can provide specific properties of an attTn7 target in vivo. Interestingly, these sequences are positioned more than 25 base pairs from the specific point of Tn7 insertion.

Base Sequence↗

PubMed1988

Tn7 transposition: two transposition pathways directed by five Tn7-encoded genes.

The bacterial transposon Tn7 is capable of high-frequency transposition to a specific site in the Escherichia coli chromosome, attTn7, and of low-frequency transposition to sites other than attTn7. Using an in vitro insertional mutagenesis procedure, we have identified and characterized five tns (Tn seven) genes that are essential for Tn7 transposition. Three of these genes, tnsA, tnsB, and tnsC, are required, but are not sufficient, for all Tn7 transposition events. In addition, tnsD is specifically required for transposition to attTn7, whereas tnsE is specifically required for transposition to other sites. Thus, Tn7 is an elaborate transposon that encodes two distinct but overlapping transposition pathways.

DNA Transposable Elements↗

PubMed1988

Recognition of Escherichia coli attTn7 by transposon Tn7: lack of specific sequence requirements at the point of Tn7 insertion.

Transposon Tn7 inserts at high frequency into a specific site in the Escherichia coli chromosome called attTn7. We show that the point of Tn7 insertion in attTn7 lies within the transcriptional terminator of the bacterial glmS gene. We have exploited the glmS transcription terminator to isolate mutants with altered sequences at the point of Tn7 insertion and have used these mutants to show that the nucleotide sequence at the point of Tn7 insertion is irrelevant to attTn7 target activity. Thus, the nucleotides which provide attTn7 target activity are distinct from the point of Tn7 insertion. We have also examined the effect of transcription on the capacity of attTn7 to act as a target for Tn7 transposition. Our results suggest that transcription of attTn7 does not modulate its Tn7 target activity.

Base Sequence↗

PubMed1987

Identification of a transposon Tn7-dependent DNA-binding activity that recognizes the ends of Tn7.

The bacterial transposon Tn7 is distinguished by its capacity for high-frequency transposition to a specific site in the Escherichia coli chromosome. tnsB is one of the five Tn7-encoded transposition genes. We have identified in vitro a tnsB-dependent DNA binding activity that interacts specifically with cis-acting transposition sequences at the Tn7 termini. Although the left and right termini of Tn7 are structurally distinct, each end contains several copies of a closely homologous 22-base-pair sequence. We present results indicating that this 22-base-pair repeat sequence is recognized by the tnsB-dependent binding activity.

Bacterial Proteins↗

PubMed1985

The role of the SPO11 gene in meiotic recombination in yeast.

Several complementary experimental approaches were used to demonstrate that the SPO11 gene is specifically required for meiotic recombination. First, sporulating cultures of spo11-1 mutant diploids were examined for landmark biochemical, cytological and genetic events of meiosis and ascosporogenesis. Cells entered sporulation with high efficiency and showed a near-doubling of DNA content. Synaptonemal complexes, hallmarks of intimate homologous pairing, and polycomplex structures appeared during meiotic prophase. Although spontaneous mitotic intra- and intergenic recombination occurred at normal levels, no meiotic recombination was observed. Whereas greater than 50% of cells completed both meiotic divisions, packaging of the four meiotic products into mature ascospores took place in only a small subset of asci. Haploidization occurred in less than 1% of viable colony-forming units. Second, the Rec- meiotic defect conferred by spo11-1 was confirmed by dyad analysis of spores derived from spo13-1 single-division meiosis in which recombination is not a requirement for viable ascospore production. Diploids homozygous for the spo13-1 mutation undergo meiotic levels of exchange followed by a single predominantly equational division and form asci containing two near-diploid spores. With the introduction of the spo11-1 mutation, high spore viability was retained, whereas intergenic recombination was reduced by more than 100-fold.

Alleles↗

PubMed1985

Meiotic exchange within and between chromosomes requires a common Rec function in Saccharomyces cerevisiae.

We used haploid yeast cells that express both the MATa and MAT alpha mating-type alleles and contain the spo13-1 mutation to characterize meiotic recombination within single, unpaired chromosomes in Rec+ and Rec- Saccharomyces cerevisiae. In Rec+ haploids, as in diploids, intrachromosomal recombination in the ribosomal DNA was detected in 2 to 6% of meiotic divisions, and most events were unequal reciprocal sister chromatid exchange (SCE). By contrast, intrachromosomal recombination between duplicated copies of the his4 locus occurred in approximately 30% of haploid meiotic divisions, a frequency much higher than that reported in diploids; only about one-half of the events were unequal reciprocal SCE. The spo11-1 mutation, which virtually eliminates meiotic exchange between homologs in diploid meiosis, reduced the frequency of intrachromosomal recombination in both the ribosomal DNA and the his4 duplication during meiosis by 10- to greater than 50-fold. This Rec- mutation affected all forms of recombination within chromosomes: unequal reciprocal SCE, reciprocal intrachromatid exchange, and gene conversion. Intrachromosomal recombination in spo11-1 haploids was restored by transformation with a plasmid containing the wild-type SPO11 gene. Mitotic intrachromosomal recombination frequencies were unaffected by spo11-1. This is the first demonstration of a gene product required for recombination between homologs as well as recombination within chromosomes during meiosis.

Chromosomes↗

PubMed1978

Discharge of the premature infant.

Appropriate interventions are initiated smoothly if the neonatal staff is familiarized with the new concepts of infant care and their empirical basis. It is also important that the nurses be present at all conferences to facilitate more meaningful interaction with the mother and her infant. If this is done, then it is easier to evaluate the needs of the mother and how much teaching support is necessary. The more involved the nurse becomes with the family, the more rewarding her experience will be, and she will be eager to get involved with the next family.

Aftercare↗