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S Swift

Publications and source records attributed to S Swift.

At least 73 records · Page 4Linked to original sources
PubMed1992

Small molecule-mediated density-dependent control of gene expression in prokaryotes: bioluminescence and the biosynthesis of carbapenem antibiotics.

Sophisticated signal transduction systems enable prokaryotes to sense their growth environment and mount an appropriate adaptive response. Signal transduction and gene regulation through the phosphorylation of two regulatory components is now recognised as one of the major global regulatory networks in bacteria. However, not all types of sensor-regulator circuits relay information via phosphoryl transfer. The Vibrio fischeri LuxR protein which has previously been characterised as a member of the response-regulator superfamily responds to a small diffusible signal molecule N-(3-oxohexanoyl)homoserine lactone (HSL). Biosynthesis of HSL in V. fischeri is dependent on the expression of the luxI gene. Until recently, the role of HSL as an 'autoinducer' was thought to be restricted to V. fischeri and a few related marine bacteria in which it controls the onset of bioluminescence. However, we have discovered that a diverse group of terrestrial bacteria: (1) produce HSL; (2) possess genes analogous to luxI; and (3) exhibit cell density-dependent induction of bioluminesence when transformed with a recombinant plasmid carrying V. fischeri lux genes but lacking luxI. In one of these, Erwinia carotovora, HSL is shown to mediate the cell density-dependent biosynthesis of a carbapenem antibiotic.

4-Butyrolactone↗
PubMed1992

The product of the mouse Xist gene is a 15 kb inactive X-specific transcript containing no conserved ORF and located in the nucleus.

The Xist gene maps to the X inactivation center region in both mouse and human, and previous analysis of the 3' end of the gene has demonstrated inactive X-specific expression, suggesting a possible role in X inactivation. We have now analyzed the entire mouse Xist gene. The mature inactive X-specific transcript is 15 kb in length and contains no conserved ORF. The Xist sequence contains a number of regions comprised of tandem repeats. Comparison with the human XIST gene demonstrates significant conservation of sequence and gene structure. Xist RNA is not associated with the translational machinery of the cell and is located almost exclusively in the nucleus. Together with conservation of inactive X-specific expression, these findings support a role for Xist in X inactivation, possibly as a functional RNA or as a chromatin organizer region.

Animals↗
PubMed1992

An SRY-related gene expressed during spermatogenesis in the mouse encodes a sequence-specific DNA-binding protein.

SRY, the testis determining gene, encodes a member of a family of DNA binding proteins characterized by an amino acid sequence motif known as the HMG box. Using degenerate primers and the polymerase chain reaction, we have isolated SRY-related cDNAs from adult murine testis RNA. One of these, Sox-5, encodes a 43 kDa HMG-box protein with similarities to transcription activating proteins. Anti-Sox-5 antibody was used to analyse expression of Sox-5 in pre-pubertal testis and in fractionated spermatogenic cells. Sox-5 is restricted to post-meiotic germ cells, being found at highest levels in round spermatids. Sox-5 is a DNA binding protein and binding site selection assays suggest that it can bind specifically to oligonucleotides containing the consensus motif AACAAT. Sry can also bind to this motif, indicating that the Sry family may have overlapping sequence specificities.

Amino Acid Sequence↗
PubMed1992

Selection and analysis of non-interactive mutants in the Escherichia coli tryptophan synthase alpha subunit.

The inherent infidelity of Taq DNA polymerase in the polymerase chain reaction was exploited to produce random mutations in the trp A gene. Screening of the resulting clones allowed selection of non-interactive mutant alpha subunits retaining their intrinsic catalytic activity. Two single changes responsible for this phenotype were identified by DNA sequencing as: alpha 126 valine (GTG)----glutamic acid (GAG) and alpha 128 valine (GTT)----aspartic acid (GAT). Three single changes giving a non-interactive phenotype with an impaired intrinsic catalytic activity were identified by DNA sequencing as alpha 66 asparagine (AAC)----aspartic acid (GAC); alpha 109 lysine (AAA)----arginine (AGA); alpha 118 cysteine (TGC)----arginine (CGC). Where possible, we individually assessed the importance of these residues in alpha beta interaction in light of structural information from X-ray crystallography and by intergeneric protein sequence comparison.

Amino Acids↗
PubMed1991

A candidate spermatogenesis gene on the mouse Y chromosome is homologous to ubiquitin-activating enzyme E1.

The human X-linked gene A1S9 complements a temperature-sensitive cell-cycle mutation in mouse L cells, and encodes the ubiquitin-activating enzyme E1. The gene has been reported to escape X-chromosome inactivation, but there is some conflicting evidence. We have isolated part of the mouse A1s9 gene, mapped it to the proximal portion of the X chromosome and shown that it undergoes normal X-inactivation. We also detected two copies of the gene on the short arm of the mouse Y chromosome (A1s9Y-1 and A1s9Y-2). The functional A1s9Y gene (A1s9Y-1) is expressed in testis and is lost in the deletion mutant Sxrb. Therefore A1s9Y-1 is a candidate for the spermatogenesis gene, Spy, which maps to this region. A1s9X is similar to the Zfx gene in undergoing X-inactivation, yet having homologous sequences on the short arm of the Y chromosome, which are expressed in the testis. These Y-linked genes may form part of a coregulated group of genes which function during spermatogenesis.

Amino Acid Sequence↗
PubMed1991

PCR based gene engineering of the Vibrio harveyi lux operon and the Escherichia coli trp operon provides for biochemically functional native and fused gene products.

The polymerase chain reaction (PCR) was applied to clone the luxA and luxB genes from Vibrio harveyi, and the trp poL (promoter operator leader) region and the trpB and trpA genes from Escherichia coli. PCR-derived luxA/B and trpB/A genes were shown to express bacterial luciferase and tryptophan synthase respectively, when introduced into E. coli on a plasmid cloning vehicle. The trp poL was used successfully to control the expression of lac alpha, luxAB, trpB and trpA. PCR was also used to construct a functional luxAB translational fusion protein. Primers for this were designed to facilitate precise gene fusion and to provide a silent mutation within an EcoRI site in the luxB gene. Production of functional genes was verified in vitro and in vivo using polyacrylamide gel electrophoresis (PAGE) analysis of transcription-translation products and crude cell extracts, and by monitoring enzyme activity.

Base Sequence↗
PubMed1990

Zfa is an expressed retroposon derived from an alternative transcript of the Zfx gene.

ZFY, a gene on the Y chromosome encoding a zinc finger protein, has been proposed as a candidate for the human testis determining gene. Sequences related to ZFY, called ZFX, are present on the X chromosome of a wide range of placental mammals. Unlike most mammals the mouse has four genes homologous to ZFY; two on the Y chromosome, Zfy-1 and Zfy-2, an X-linked gene, Zfx, and an autosomal gene, Zfa. We show here that Zfa has arisen recently by retroposition of one of at least three alternatively spliced mRNAs transcribed from the Zfx gene. Zfa is an unusual retroposon in that it has retained an open reading frame and is expressed, although its function may be limited or altered by the presence of a potentially inactivating mutation in the third of its zinc fingers. This mutation must have occurred at the same time or soon after the retroposition event as it is also present in the Zfa gene of Mus spretus. Interestingly the third finger of the M. musculus musculus Zfy-2 gene has also sustained a mutation suggesting that this gene family may be rapidly evolving in mice.

Amino Acid Sequence↗
PubMed1989

Growth factor independence and indefinite growth ("immortalization") appear simultaneously after crisis in murine myelocytes expressing v-myc.

In murine myelocytes doubly infected with the v-myc virus and the v-Ha-ras virus, or the v-myc virus and the v-abl virus, the emergence of growth factor-independent cells is a rare event which coincides with crisis in the cultures. All growth factor-independent cells which emerge from crisis are also "immortalized", i.e., able to grow indefinitely. We wanted to determine whether the v-abl gene plays a role in the immortalization of the growth factor-independent cells. Therefore we infected murine myelocytes with v-myc virus and a v-abl mutant virus coding for a temperature-sensitive tyrosine kinase. Growth factor-independent cell clones were isolated and their properties at the nonpermissive temperature analyzed. We observed that 4 hr after the shift to the nonpermissive temperature the expression of both the genomic and subgenomic viral v-myc transcripts decreased significantly, followed by a loss of the viability of the cells. However, several variants emerged which were able to grow at the nonpermissive temperature and showed elevated expression of v-myc. The results suggest: 1) that v-abl plays a role in the immortalization of the cell clones by maintaining a critical level of v-myc expression; 2) that rare genetic changes leading to constitutive v-myc expression independent of v-abl tyrosine kinase activity can also lead to immortalization in this model system, and 3) that immortalization and growth factor independence occur in post-crisis cells and are associated with constitutive expression of v-myc.

Animals↗
PubMed1988

Glycosylated haemoglobin: an index of glucose control in pancreatic islet transplanted rats.

In this study we have measured glycosylated haemoglobin in the blood of 22 rats made diabetic with streptozotocin. This significantly increased from a normal level of 1.6 +/- 0.2% to reach a maximum, plateau level, of 6.6 +/- 0.3% at 45 days. At this time, 16 of these animals were given intra-portal transplants of purified isologous pancreatic islets. By varying the number of islets transplanted, animals were produced with normal blood glucose levels on random sampling, but with a spectrum of glucose control as measured by the glucose tolerance test. The glycosylated haemoglobin level was also measured at 30, 60 and 120 days post transplantation. This was significantly reduced (in some cases back to normal) and at 60 and 120 days there was a significant correlation (p less than 0.001) between glycosylated haemoglobin and the glucose clearance (K value). These results suggest that the measurement of glycosylated haemoglobin can be used as a simple and accurate index of glucose metabolism in islet transplanted rats.

Animals↗
PubMed1987

The induction of growth factor-independence in murine myelocytes by oncogenes results in monoclonal cell lines and is correlated with cell crisis and karyotypic instability.

Infection of established (IL-3)-dependent hematopoietic cell lines with Abelson murine leukemia virus (A-MLV) abrogates their requirement for IL-3 and leads to non-autocrine growth factor-independent cells. We were interested to determine whether A-MLV can induce IL-3 independence also in non-established cells. To obtain long-term cultures of diploid myelocytes, splenic hematopoietic cells were first infected with MMCV, a murine retrovirus carrying the avian v-myc oncogene. These cultures were superinfected with A-MLV. In three independent experiments, the first growth factor-independent cells appeared between 18 and 43 days after superinfection with A-MLV and represented .02-1% of the population. Furthermore, the cultures that became growth factor-independent were monoclonal for integration of the v-abl gene. These results indicate that the acquisition of growth factor-independence after superinfection of v-myc-expressing cells with A-MLV is a rare event. The low frequency of growth factor-independent cells was not due to a low percentage of infected cells, since 15-25% of the cells were infected with A-MLV after 7 days. The first appearance of growth factor-independent cells coincided with crisis in the cultures, as indicated by a high incidence of cell death and a reduced overall growth rate of the cell populations. These growth factor-independent cells exhibited variable karyotypes, including many that were near-triploid to near-tetraploid. In summary, growth factor-independence induced by super-infection with A-MLV, like that induced by double-infection with v-myc- and v-H-ras-containing viruses, is associated with unstable karyotypes. The growth factor-independent cells show variable ploidy characteristic of cells which survived crisis.

Animals↗
PubMed1986

Specific sequences of the env gene determine the host range of two XC-negative viruses of the Rauscher virus complex.

Two viruses which do not give rise to XC plaques in the standard XC assay (XC-negative) have been isolated from the Rauscher virus (RV) complex. These viruses differ in their host range. One, R-MCF-1, is dualtropic and will therefore infect both murine and non-murine cells. However, unlike other mink cell focus-inducing (MCF) viruses, it cannot infect NIH 3T3 cells. The other, R-XC-, is ecotropic. It will infect murine cells, including NIH 3T3 cells, but does not infect mink lung cells. Analysis of hybrid viruses, in which homologous regions of the genomes of R-MCF-1 and R-XC- virus were exchanged, indicated that the NH2-terminal portion of the gp70 is responsible for the particular host ranges of these viruses. The nucleotide sequence of the env gene of R-XC- virus was therefore determined and compared with the known env sequences of ecotropic MLVs and dualtropic MCF viruses of the Rauscher and Friend virus complexes. R-XC- virus was found to be a recombinant virus. Its env gene contained sequences derived from an endogenous env gene which were closely related to those of the MCF viruses but differed from any previously described sequences. The particular properties of R-MCF-1 and R-XC- virus suggest that the two viruses arose by recombination between R-MLV and two endogenous env sequences which differ from those of the known MCF viruses. If so, this suggests that the mouse genome contains at least five env sequences which can give rise to MCF-like viruses. In addition, since the host range and interference properties of R-XC- virus are very similar to those of the previously described ecotropic recombinant viruses, it may be that the ecotropic recombinant viruses arose by recombination with the same endogenous env sequences as did R-XC- virus.

Animals↗
PubMed1985

Envelope gene and long terminal repeat determine the different biological properties of Rauscher, Friend, and Moloney mink cell focus-inducing viruses.

The nucleotide sequence of the envelope (env) gene and the long terminal repeat (LTR) of an infectious clone of Rauscher mink cell focus-inducing (R-MCF) virus has been determined and compared with the published env gene and LTR sequences of Friend (F)- and Moloney (M)-MCF viruses. The sequence shows that R-MCF virus, like other MCF viruses, is a recombinant virus. Its env gene contains sequences which were acquired from an env gene in the mouse genome and which confer on the MCF virus its dualtropic host range. Unlike F-MCF and M-MCF viruses, R-MCF virus will not replicate in NIH 3T3 cells. The deduced amino acid sequence for the gp70 of R-MCF differs from that of F- and M-MCF viruses by 15 amino acids between residues 49 and 138 of gp70. These differences in amino acid sequences may be responsible for the inability of R-MCF virus to replicate in NIH 3T3 cells. The host range of two hybrid viruses constructed in vitro is consistent with this hypothesis. R-MCF virus and Friend murine leukemia virus (F-MLV) show 98% identity in their env gene 3' from the acquired env sequences. This contrasts with 82% identity between the env gene of R-MCF virus and M-MLV. The LTR of R-MCF shows 98% identity with the LTR of F-MCF as compared to 88% identity with the LTR of M-MCF. This striking similarity between the sequences of R-MCF, F-MCF, and F-MLV is surprising since the Rauscher virus and the Friend virus are thought to have originated independently. The high degree of similarity suggests that Rauscher and Friend viruses have a common origin. In contrast to M-MLV, which induces predominantly a lymphoid disease, R- and F-MCF viruses induce an erythroproliferative disease in NIH Swiss mice. A hybrid R-MCF virus with a genome derived primarily from R-MCF virus and a 3' end including the U3 region derived from M-MLV induces a lymphoid disease instead of an erythroid disease. This result indicates that it is the U3 region which determines the tissue specificity of the MCF virus-induced disease. It is suggested that the putative viral enhancers in the U3 region play two roles in the process of leukemogenesis: in the Friend and Rauscher disease, the viral enhancers act by increasing the transcription of the MCF env gene; in the thymic lymphoma, the enhancers activate mainly the expression of cellular genes.

Amino Acid Sequence↗
PubMedDate not supplied

Role of flhDC in the expression of the nuclease gene nucA, cell division and flagellar synthesis in Serratia marcescens.

We investigated in Serratia marcescens the functions of the flhDC operon, which controls motility and cell division in enteric bacteria. Included in our evaluations were investigation of cell division, flagellar synthesis and regulation of the expression of nuclease (encoded by the nucA(Sm) gene, one of the virulence factors). Interruption of the chromosomal flhDC operon in S. marcescens CH-1 resulted in aberrant cell division and loss of nuclease and flagella. Expression of nucA(Sm) and other mutated phenotypes was restored in the flhDC mutant by the induction of overexpression of flhDC in a multicopy plasmid. Multicopied flhDC also induced the formation of differentiated cells (polyploid aseptate cells with oversynthesis of peritrichous flagella) in broth culture using minimal growth medium. Expression of the flhDC operon showed positive autoregulation, and was growth phase dependent (upregulated in early log phase). In addition, flhDC expression was inhibited when the temperature increased from 30 to 37 degrees C, and when osmolarity was increased, but was not influenced by glucose catabolite repression. These results show that FlhD/FlhC is a multifunctional transcriptional activator involved in the process of cell differentiation, swarming and virulence factor expression.

Amino Acid Sequence↗