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G J Liaw

Publications and source records attributed to G J Liaw.

13 recordsLinked to original sources
PubMed2000

A missense mutation in the nuclear gene coding for the mitochondrial aspartyl-tRNA synthetase suppresses a mitochondrial tRNA(Asp) mutation.

The nuclear suppressor allele NSM3 in strain FF1210-6C/170-E22 (E22), which suppresses a mutation of the yeast mitochondrial tRNA(Asp)gene in Saccharomyces cerevisiae, was cloned and identified. To isolate the NSM3 allele, a genomic DNA library using the vector YEp13 was constructed from strain E22. Nine YEp13 recombinant plasmids were isolated and shown to suppress the mutation in the mitochondrial tRNA(Asp)gene. These nine plasmids carry a common 4. 5-kb chromosomal DNA fragment which contains an open reading frame coding for yeast mitochondrial aspartyl-tRNA synthetase (AspRS) on the basis of its sequence identity to the MSD1 gene. The comparison of NSM3 DNA sequences between the suppressor and the wild-type version, cloned from the parental strain FF1210-6C/170, revealed a G to A transition that causes the replacement of amino acid serine (AGU) by an asparagine (AAU) at position 388. In experiments switching restriction fragments between the wild type and suppressor versions of the NSM3 gene, the rescue of respiratory deficiency was demonstrated only when the substitution was present in the construct. We conclude that the base substitution causes the respiratory rescue and discuss the possible mechanism as one which enhances interaction between the mutated tRNA(Asp)and the suppressor version of AspRS.

Alleles↗
PubMed1999

A common mechanism for antenna-to-Leg transformation in Drosophila: suppression of homothorax transcription by four HOM-C genes.

The Drosophila HOM-C genes encode transcription factors containing the DNA-binding homeodomain. Mutations in the HOM-C genes can cause specific homeotic transformation, suggesting that the HOM-C genes determine segmental identities by acting on different target genes. However, misexpression of several HOM-C genes in the antenna disc causes similar antenna-to-leg transformations. Here we show that the Scr, Antp, Ubx, and abd-A HOM-C genes all exert their effects through a common mechanism: suppressing the transcription of the homothorax (hth) homeobox gene and thereby preventing the nuclear localization of the Extradenticle homeodomain protein. We also show that ectopic hth expression can cause duplication of the proximodistal axis of the antenna, suggesting that it is involved in proximodistal development of the antenna.

Animals↗
PubMed1999

Investigation of an outbreak of Pseudomonas putida using antimicrobial susceptibility patterns, pulsed-field gel electrophoresis of genomic DNA and restriction fragment length polymorphism of PCR-amplified rRNA operons.

Seventeen Pseudomonas putida isolates were investigated which were collected from the urine specimens of 14 patients and one reflectrometer by comparing antimicrobial susceptibility patterns, pulsed-field gel electrophoresis (PFGE) of genomic DNA, and restriction fragment length polymorphism (RFLP) of PCR-amplified rRNA operons. Three susceptibility patterns were defined by testing 22 antimicrobial agents, with 14 isolates resistant to all agents. PFGE of XbaI-genomic DNA fragments divided the 17 isolates into 9 distinct types. One type, seen in 6 isolates showing identical patterns of approximately 35 fragments of 10 to 350 kb, was defined as the outbreak strain. Another 4 types, in a total of 6 isolates, were considered closely related to the outbreak strain; 2 types in 1 isolate each were possibly related to the outbreak strain; and 2 types in a total of 3 isolates were different from the outbreak strain. All 12 outbreak or closely related isolates were from patients in the surgical intensive care unit and a surgical ward, and were different from isolates in other wards, clearly indicating an outbreak of P. putida. Only two types were defined by the RFLP of 4.5 kb PCR-amplified rRNA operons; one type was seen in 15 isolates, while the other was seen in only 2 isolates. In conclusion, PFGE of genomic DNA is a highly discriminatory and reproducible method for epidemiological typing of P. putida.

DNA, Bacterial↗
PubMed1999

Rapid detection of herpes simplex virus by polymerase chain reaction.

This study reports the successful use of three sets of primers, each from different genes on the herpes simplex virus (HSV) genome, 1) the DNA polymerase gene, 2) the glycoprotein B gene, and 3) the glycoprotein D gene, for detection of HSV DNA by polymerase chain reaction (PCR). All three sets of primers detected the same HSV DNA in the throat and genital specimens. Using the conventional viral culture as a standard, PCR provided a sensitivity of 100% and a specificity of 100% in this study. In addition, a nested-PCR protocol using two sets of primers in the glycoprotein D gene, one set internal to the other, was evaluated for the amplification of HSV DNA in cerebrospinal fluid (CSF) from patients suspected of having herpes simplex encephalitis (HSE). Five of the 10 CSF specimens tested were found positive. In conclusion, PCR detection is a valuable tool for rapid diagnosis of HSV infection, especially for CSF specimens.

Cells, Cultured↗
PubMed1997

Control of early neurogenesis of the Drosophila brain by the head gap genes tll, otd, ems, and btd.

The progenitors of the Drosophila central nervous system (CNS), called neuroblasts, segregate from the neurectoderm of the early embryo in a stereotyped pattern. The neuroblasts that give rise to the brain segregate from the procephalic neurectoderm and form three neuromeres, called protocerebrum, deuterocerebrum, and tritocerebrum. The expression of the proneural genes of the achaete-scute complex (AS-C) is required for neurectodermal cells to acquire the competency to form neuroblasts. We show here that the expression of the proneural gene lethal of scute (l'sc) is required for the development of the majority of the procephalic neuroblasts. l'sc expression in the procephalic neurectoderm is controlled by the head gap genes tailless (tll), orthodenticle (otd), buttonhead (btd), and empty spiracles (ems), which are expressed in partially overlapping domains of the head neurectoderm. Loss of function of a given head gap gene results in the absence of l'sc expression in its domain, followed by the absence of neuroblasts that would normally segregate from this domain. Loss of tll function results in the absence of all protocerebral neuroblasts, otd functions in a domain that includes a large part of the protocerebrum and a smaller part of the adjacent deuterocerebrum. Both ems and btd are required in partially overlapping subsets of neuroblasts of the deuterocerebrum and tritocerebrum.

Animals↗
PubMed1997

Complex regulatory region mediating tailless expression in early embryonic patterning and brain development.

tailless encodes a transcription factor expressed in multiple domains in the developing embryo. Early and transient expression at the posterior pole is required to establish a domain from which the eighth abdominal segment, telson and posterior gut arise. Just a few nuclear cycles later, a brain-specific domain is initiated at the anterior; expression in this domain is maintained with complex modulations throughout embryogenesis. Expression of tailless in this domain is required to establish the most anterior region of the brain. To understand the function and regulation of these different domains of expression, we provide a detailed description of tailless expression in brain neuroblasts and show that this expression is not detectably regulated by the head gap genes buttonhead or orthodenticle, by the proneural gene lethal of scute or by tailless itself. We show that approximately 6 kb of sequenced upstream regulatory DNA can drive lacZ expression in a pattern that mimics the full tailless embryonic expression pattern. Within this sequence we identify multiple modules responsible for different aspects of the tailless pattern. In addition to identifying additional torso response elements that mediate early blastoderm polar expression, we show that the complex brain expression pattern is driven by a combination of modules; thus expression at a low level throughout the brain and at a high level in the dorsal medial portion of the brain and in the optic lobe, as well as neuroblast-specific repression are mediated by different DNA regions.

Animals↗
PubMed1995

The torso response element binds GAGA and NTF-1/Elf-1, and regulates tailless by relief of repression.

Modulation of transcription factor activity leading to changes in cell behavior (e.g., differentiation versus proliferation) is one of the critical outcomes of receptor tyrosine kinase (RTK) stimulation. In the early Drosophila embryo, activation of the torso (tor) RTK at the poles of the embryo activates a phosphorylation cascade that leads to the spatially specific transcription of the tailless (tll) gene. Our analysis of the tor response element (tor-RE) in the tll promoter indicates that the key activity modulated by the tor RTK pathway is a repressor present throughout the embryo. We have mapped the tor-RE to an 11-bp sequence; using this sequence as the basis for protein purification, we have determined that the proteins GAGA and NTF-1 (also known as Elf-1, product of the grainyhead gene) bind to the tor-RE. We demonstrate that NTF-1 can be phosphorylated by MAPK (mitogen-activated protein kinase), and that tll expression is expanded in embryos lacking maternal NTF-1 activity; these results make NTF-1 a likely target for modulation by the tor RTK pathway in vivo. The data presented here support a model in which activation of the tor RTK at the poles of the embryos leads to inactivation of the repressor and therefore, to transcriptional activation (by activators present throughout the embryo) of the tll gene at the poles of the embryo.

Animals↗
PubMed1995

Binding sites for transcription factor NTF-1/Elf-1 contribute to the ventral repression of decapentaplegic.

The Dorsal morphogen is a transcription factor that activates some genes and represses others to establish multiple domains of gene expression along the dorsal/ventral axis of the early Drosophila embryo. Repression by Dorsal appears to require accessory proteins that bind to corepression elements in Dorsal-dependent regulatory modules called ventral repression regions (VRRs). We have identified a corepression element in decapentaplegic (dpp), a zygotically active gene that is repressed by the Dorsal morphogen. This dpp repression element (DRE) is located within a previously identified VRR and close to essential Dorsal-binding sites. We have purified a factor from Drosophila embryo extracts that binds to the DRE but not to mutant forms of the DRE that fail to support efficient repression. This protein also binds to an apparently essential region in a VRR associated with the zerknüllt (zen) gene. One of the DREs in the dpp VRR overlaps the binding site for a potential activator protein suggesting that one mechanism of ventral repression may be the mutually exclusive binding of repressor and activator proteins. We have found the DRE-binding protein to be identical to NTF-1 (equivalent to Elf-1, the product of the grainyhead gene), a factor originally identified as an activator of the Ultrabithorax and Dopa decarboxylase promoters. NTF-1 mRNA is synthesized during oogenesis and deposited in the developing oocyte where it is available to contribute to ventral repression during early embryogenesis. Previous studies have shown that overexpression of NTF-1 in the postblastoderm embryo results in a phenotype that is consistent with a role for this factor in the repression of dpp later in embryogenesis.

Animals↗
PubMed1993

Characterization of downstream elements in a Raf-1 pathway.

At the poles of the Drosophila embryo, cell fate is established by a pathway that begins with the activation of a membrane-associated tyrosine kinase (the torso gene product); this then leads to activation of a serine/threonine kinase (Drosophila Raf-1). Activated Raf-1 then leads, by an undefined mechanism, to the transcriptional activation of the tailless (tll) gene; the tll gene product, itself a transcription factor, subsequently regulates the expression of an array of target genes. To further define this pathway, we have utilized sequence comparison between Drosophila melanogaster and Drosophila virilis to identify conserved elements in the tll promoter region. As assessed by DNase I footprinting and promoter dissection experiments, two of these elements are potential regulatory targets of Raf-1-activated transcription factors. Sequence comparison also reveals that the unique residues in the DNA-binding domain of the tll protein, the next component in the pathway, are conserved. One of these residues, the alanine after the last cysteine in the first zinc finger, may be responsible for part of the difference between the tll protein DNA binding site and the closely related half-site of the retinoid/estrogen receptors. Consistent with the rapid turnover of the tll protein, it contains a PEST sequence (rich in proline, glutamate and aspartate, serine, and threonine) that is also conserved.

Amino Acid Sequence↗
PubMed1993

Control of tailless expression by bicoid, dorsal and synergistically interacting terminal system regulatory elements.

Three different maternal morphogen gradients regulate expression of the gap gene tailless (tll), which is required to establish the acron and telson of the Drosophila embryo. To identify elements in the tll promoter that respond to these different maternal systems, we have generated promoter-lacZ fusions and transformed them into the germline. Expression of these constructs in both wild type and mutant embryos revealed the presence of at least two separate but synergistically interacting regions that mediate tll expression by the terminal system. This functional synergism between regulatory elements may play a role in the translation of the torso (tor) morphogen gradient into the sharp boundary of tll gene activity. In addition to regions mediating activation by the terminal system, regions mediating both activation and repression by bicoid (bcd), and repression by dorsal (dl) were identified. Binding sites of bcd protein in a 0.5 kb region, revealed by DNaseI footprinting, could be crucial for the bcd-dependent activation of tll expression in the anterior stripe.

Animals↗
PubMed1991

Dual role of the Drosophila pattern gene tailless in embryonic termini.

One of the first zygotically active genes required for formation of the terminal domains of the Drosophila embryo is tailless (tll). Expression of the tll gene is activated ectopically in gain-of-function mutants of the maternal terminal gene torso (tor); this suggests that tor normally activates the tll gene in the termini. Ectopic expression of tll under the control of an inducible promoter results in differentiation of ectopic terminal-specific structures, the Filzkörper, and leads to the activation of at least one gene, hunchback, that is required to form these structures. Ectopic expression of the tll gene also represses segmentation by repressing the gap genes Krüppel and knirps and probably also pair rule genes.

Animals↗
PubMedDate not supplied

Utilization of Drosophila eye to probe the functions of two mammalian serine/threonine kinases, Snk and HsHPK.

Here we report a quick functional analysis of two mammalian serine/threonine kinases, a serum inducible kinase (Snk) and Homo sapiens hepatoma protein kinase (HsHPK), using Drosophila eye as a model system. We generated transgenic fly lines carrying constructs of both kinases under control of the GAL upstream activating sequence (UAS). Each UAS line was then crossed to a line in which GAL4 expression was driven by one of the following promoters, eyeless (ey), glass or decapentaplegic. Thus, different kinase mutants can be ectopically expressed in a promoter-dependent manner. We observed that the ectopic expression of either the wild-type or active form of Snk driven by the glass promoter resulted in a rough-eye phenotype. Nevertheless, the ectopic expression of HsHPK under the control of the ey promoter resulted in a small-eye phenotype. The results of this study demonstrated that ectopic expression of these two mammalian genes could be achieved by the regulation of Drosophila promoters. In addition, the effects of these ectopically expressed genes on eye development could be an implication of their functions with respect to cell proliferation and differentiation. Thus, Drosophila eye, with the powerful genetic tools and vast information on eye development available, can be a useful system to probe the functions of mammalian genes in the postgenome era.

Animals↗