Chromosomal sequences flanking an efficiently expressed transgene dramatically enhance its expression

The expression of transgenes in mice is influenced strongly by their site of integration in the genome. To test whether the chromosomal sequences immediately flanking a site of integration could positively influence expression we isolated the 5' and 3' chromosomal sequences from an efficiently expressed transgenic locus. These chromosomal sequences were incorporated into transgene constructs and these were then introduced into mice. Linking them to the original transgene dramatically enhanced its expression and conferred a degree of position independent expression upon it. However, the results were not as marked when these sequences were linked to other constructs, showing that the effectiveness of such flanking chromosomal sequences is highly dependent on the nature of the transgene used.     

The urea amidolyase (DUR1,2) gene of Saccharomyces cerevisiae.

The DNA sequence of the urea amidolyase (DUR1,2) gene from S. cerevisiae has been determined. The polypeptide structure deduced from the DNA sequence contains 1,835 amino acid residues and possesses a calculated weight of 201,665 daltons which favorably correlates with that predicted from compositional analysis of purified protein (1,881 amino acid residues and a molecular weight of 203,900). The C-terminal 57 residues of the polypeptide exhibit significant homology with similarly situated sequences found in five other biotin carboxylases whose primary structures have been determined or deduced from protein and DNA sequence data, respectively. Major S1 nuclease protection fragments derived from DUR1,2 RNA-DNA hybrids exhibit apparent termini at positions -140 and -141 upstream of the coding region. The termini of minor protection fragments also occur at eleven other positions as well.     

Analysis of mutations affecting Ty-mediated gene expression in Saccharomyces cerevisiae

Summary Yeast translocatable, Ty, elements can cause constitutive synthesis of the glucose-repressible alcohol dehydrogenase (ADHII) when inserted upstream from the 5 end of the structural gene, ADR2. These insertion mutations, ADR3 ^c, are unstable and give rise to secondary ADHII^– mutations. The majority of such mutants, adr3, can be attributed to excision of the insertion sequence, leaving behind a single copy of the -sequence which occurs as a direct repeat at the ends of the Ty elements. A few adr3 mutants appear to be generated by DNA-rearrangements in the vicinity of the Ty insertion. The occurrence of recessive mutants, tye, which are unlinked to ADR2 indicates that the constitutive expression of ADR2 caused by the Ty insertions requires the function of trans-acting genes. These results support the idea that regulation of Ty-linked ADR2 is actively mediated by the insertion sequence and is probably not due to a mere disruption of the wild-type controlling site.     

促性腺激素释放激素受体及其基因表达调控

促性腺激素释放激素（ＧｎＲＨ,ＬＨＲＨ）在体内的重要功能是由ＧｎＲＨ受体介导的。ＧｎＲＨ受体是近年神经分内分泌和生殖生物学研究的热点之一,本文从ＧｎＲＨ受体的分子结构,ＧｎＲＨ受体基因表达调控,ＧｎＲＨ受体分布及表达,调节ＲｎＲＨ受体的因素以及ＧｎＲＨ受体介导的细胞信号转导等几个方面对ＧｎＲＨ受体近年来的研究进展进行了综述,对ＧｎＲＨ受体的研究,将有助于人们进一步了解ＧｎＲＨ受体在生殖调节和恶性肿     

Decorin gene expression and its regulation in human keratinocytes

In various cell types, including cancer cells, decorin is involved in regulation of cell attachment, migration and proliferation. In skin, decorin is seen in dermis, but not in keratinocytes. We show that decorin gene (DCN) is expressed in the cultured keratinocytes, and the protein is found in the cytoplasm of differentiating keratinocytes and in suprabasal layers of human epidermis. RT-PCR experiments showed that DCN expression is regulated by pro-inflammatory and proliferative cytokines. Our data suggest that decorin should play a significant role in keratinocyte terminal differentiation, cutaneous homeostasis and dermatological diseases.     

Characterisation of mutations in the Klebsiella pneumoniae nitrogen fixation regulatory gene nifL which impair oxygen regulation

The nifL gene product of Klebsiella pneumoniae inhibits the activity of the positive activator protein NifA in response to increased levels either of fixed nitrogen or of oxygen in the medium. In order to demonstrate that the responses to these two effectors are discrete we have subjected nifL to hydroxylamine mutagenesis and isolated nifL mutants that are impaired in their ability to respond to oxygen but not to fixed nitrogen. Two such mutations were sequenced and shown to be single base pair changes located in different parts of nifL. The amino acid sequence of NifL shows limited homology to the histidine protein kinases which comprise the sensing component of bacterial two-component regulatory systems. In the light of the location of one of the oxygen-insensitive mutations (Leu294Phe) we have reassessed this homology and we suggest that the Gln273-Leu317 region of NifL may facilitate interactions between NifL and NifA.Abbreviations X-gal 5-bromo-4-chloro-3-indolyl--D-galactopy-ranoside - USAs upstream activator sequences     

Ribozymes, riboswitches and beyond: regulation of gene expression without proteins

Although various functions of RNA are carried out in conjunction with proteins, some catalytic RNAs, or ribozymes, which contribute to a range of cellular processes, require little or no assistance from proteins. Furthermore, the discovery of metabolite-sensing riboswitches and other types of RNA sensors has revealed RNA-based mechanisms that cells use to regulate gene expression in response to internal and external changes. Structural studies have shown how these RNAs can carry out a range of functions. In addition, the contribution of ribozymes and riboswitches to gene expression is being revealed as far more widespread than was previously appreciated. These findings have implications for understanding how cellular functions might have evolved from RNA-based origins.     

Mendelian and non-mendelian mutations affecting surface antigen expression in Paramecium tetraurelia.

A screening procedure was devised for the isolation of X-ray-induced mutations affecting the expression of the A immobilization antigen (i-antigen) in Paramecium tetraurelia. Two of the mutations isolated by this procedure proved to be in modifier genes. The two genes are unlinked to each other and unlinked to the structural A i-antigen gene. These are the first modifier genes identified in a Paramecium sp. that affect surface antigen expression. Another mutation was found to be a deletion of sequences just downstream from the A i-antigen gene. In cells carrying this mutation, the A i-antigen gene lies in close proximity to the end of a macronuclear chromosome. The expression of the A i-antigen is not affected in these cells, demonstrating that downstream sequences are not important for the regulation and expression of the A i-antigen gene. A stable cell line was also recovered which shows non-Mendelian inheritance of a macronuclear deletion of the A i-antigen gene. This mutant does not contain the gene in its macronucleus, but contains a complete copy of the gene in its micronucleus. In the cytoplasm of wild-type animals, the micronuclear gene is included in the developing macronucleus; in the cytoplasm of the mutant, the incorporation of the A i-antigen gene into the macronucleus is inhibited. This is the first evidence that a mechanism is available in ciliates to control the expression of a gene by regulating its incorporation into developing macronuclei.