Carbon-starvation induction of the ugp operon, encoding the binding protein-dependent sn-glycerol-3-phosphate transport system in Escherichia coli.

Summary The gene products of the ugp operon of Escherichia coli are responsible for the uptake of sn-glycerol-3-phosphate and certain glycerophosphodiesters. The regulation of ugp is mainly phoBR-dependent. Significant expression, however, can be observed even in the presence of high concentrations of phosphate, a condition which normally completely represses pho expression. Pho-independent ugp expression was found to be derepressed during the late logarithmic growth phase due to carbon starvation. Among different carbon sources tested, glucose caused the most complete repression. Addition of cAMP prevented glucose repression, indicating that a cAMP-CRP control mechanism may be directly or indirectly involved in the carbon-starvation response. This conclusion is supported by the fact that pho-independent ugp expression correlated with the presence of the cya and crp gene products.     

In vivo ionizing irradiations produce deletions in the hprt gene of human T-lymphocytes

The hprt T-lymphocyte cloning assay, which detects mutations occurring in vivo in humans, has been used to examine mutants induced in patients receiving radioimmunoglobulin therapy (RIT) for cancer. Samples from 13 patients before treatment (controls) and 15 samples from 12 patients after treatment were studied for both mutant frequencies and molecular changes in the hprt mutant T-cell clones. Patients were studied up to 48 months after treatment. Post-RIT patients showed increased mutant frequencies as compared to pre-treatment values. T-cell receptor (TCR) gene analysis of mutant T-cell clones demonstrated that 84% arose independently, both pre- and post-treatment, which is the same proportion as seen in normal individuals. However, several individuals did show large sets of mutants with the same TCR gene rearrangement patterns. Molecular analysis of mutants demonstrated a greater proportion of mutations with hprt gene changes on Southern blots after RIT treatment than before (40% versus 20%). RIT increases the proportion of mutations with total rather than partial gene deletions or other gross structural changes compared to normal individuals or pre-treatment patients. These studies are defining the spectrum for radiation-induced hprt gene mutations in vivo in human T-lymphocytes.     

Expression in yeast of a cDNA copy of the K2 killer toxin gene

Summary A cDNA copy of the M2 dsRNA encoding the K2 killer toxin ofSaccharomyces cerevisiae was expressed in yeast using the yeastADH1 promoter. This construct produced K2-specific killing and immunity functions. Efficient K2-specific killing was dependent on the action of the KEX2 endopeptidase and the KEX1 carboxypeptidase, while K2-specific immunity was independent of these proteases. Comparison of the K2 toxin sequence with that of the K1 toxin sequence shows that although they share a common processing pathway and are both encoded by cytoplasmic dsRNAs of similar basic structure, the two toxins are very different at the primary sequence level. Site-specific mutagenesis of the cDNA gene establishes that one of the two potential KEX2 cleavage sites is critical for toxin action but not for immunity. Immunity was reduced by an insertion of two amino acids in the hydrophobic amino-terminal region which left toxin activity intact, indicating an independence of toxin action and immunity.     

Identification of a new gene in an operon for cellulose biosynthesis in Acetobacter xylinum

DNA sequencing of the region downstream of the cellulose synthase catalytic subunit gene of Acetobacter xylinum led to the identification of an open reading frame coding for a polypeptide of 86 kDa. The deduced amino acid sequence of this polypeptide matches from position 27 to 40 with the N-terminal amino acid sequence determined for a 93 kDa polypeptide that copurifies with the cellulose synthase catalytic subunit during purification of cellulose synthase. The cellulose synthase catalytic subunit gene and the gene encoding the 93 kDa polypeptide, along with other genes probably, are organized as an operon for cellulose biosynthesis in which the first gene is the catalytic subunit gene and the second gene codes for the 93 kDa polypeptide. The function of the 93 kDa polypeptide is not clear at present, however it appears to be tightly associated with the cellulose synthase catalytic subunit. Sequence analysis of the polypeptide shows that it is a membrane protein with a signal sequence at the N-terminal end and a transmembrane helix in the C-terminal region for anchoring it into the membrane.     

Relative importance of size versus territorial residency in intraspecific aggression by symbiotic male water mites (Acari: Unionicolidae)

Body size plays an important role in the outcome of aggressive encounters between males of the symbiotic freshwater miteUnionicola formosa. Since intruding males displace resident males as often as resident males successfully defend their territory (mantle cavity of a mussel), resident males do not hold a competitive advantage during male-male aggressive encounters. Larger male size probably enhances a male's success when competing for receptive females.     

Oestrogen receptor gene structure and function in breast cancer

The mechanisms underlying loss of oestrogen responsiveness in breast cancer are not well-defined. Potential mechanisms include loss of receptor expression, alterations in the oestrogen receptor (ER) gene producing proteins with abnormal function, or changes to receptor-dependent or -independent pathways controlling cell proliferation. Examination by Southern analysis of the ER gene in a series of ER-negative and -positive breast tumour biopsies failed to provide evidence of gross rearrangements and in only only one of thirty seven tumour DNA samples was significant gene amplification observed. No restriction fragment length polymorphisms were detected for the restriction enzymes EcoRI, Pst I or Hind III. Methylation of the ER gene as assessed by Hpa II and Msp I restriction enzyme digests varied between tumours but the degree of methylation was not correlated with levels of expression of the receptor protein. Similar findings applied in a series of ER-negative and -positive breast cancer cell lines and clonal lines of MCF-7 cells, which were developed as an in vitro model for the acquisition of oestrogen and antioestrogen resistance. In this model there was no evidence that changes to ER receptor function and/or structure at the level of the ER gene, mRNA, ligand binding, and ability to induce progesterone receptor might account for the development of hormone resistance. However, the ability of ER to interact with a DNA sequence containing the vitellogenin promoter oestrogen response element, as assessed by gel retardation assay, was impaired in the clone showing the greatest degree of oestrogen and antioestrogen resistance.     

The acetycholinesterase gene ofAnopheles stephensi

1. The acetylcholinesterase (AChE) gene from the important malaria vector Anopheles stephensi has been isolated by homology to the Drosophila acetylcholinesterase gene. 2. The complete sequence and intron-exon organization has been determined. The encoded protein has 69% identity to Drosophila AChE and 38 and 36% identity to Torpedo AChE and human butyrylcholinesterase, respectively.     

Capacity of neural crest cells from various axial levels to participate in thymic development

Summary In order to assess the capacity of neural crest from different sources to participate in thymic development, neural crest from selected axial levels was transplanted unilaterally from quail donors to the region in chick hosts from which neural crest cells normaly migrate to interact with the primordial thymus. The greatest representation of donor cells was observed after isotopic transplantation and when donor tissue was taken from the hyoid and mesencephalic regions of the neural crest. The capacity for transplants to contribute cells decreased both anteriorly and posteriorly, so that neural crest close to the usual origin of mesenchyme-producing cells contributed a larger number of donor cells around the developing thymus than neural crest from anterior and posterior regions. Cells from the transplant were inserted as an addition to the host chick cells. Thus, a special relationship and capacity for interaction in thymic development is expressed by neural crest at usual levels over a limited span of axial regions, but to some extent by all regions. This study has established that the capacity for neural crest cells from different axial levels to interact with developing organs is not uniform, but may vary, depending upon the nature of the interaction with a particular organ.This study was supported by Grant No. 2332, The Council for Tobacco Research, USA, Inc.     

Maturation-related changes in mass and elemental contents of secretory granules as measured by electron-microprobe

Summary The relationship between granule density, protein content, and Ca and S contents were studied in two secretory granule fractions, from parotid glands of the rat, previously shown to constitute different stages in granule maturation. The density of the lighter fraction was between 1.133 and 1.142 g/ml, while that of the heavier fraction was greater than 1.142 g/ml. The mean protein content of the denser granules was 12% greater than that of the lighter granules (P<0.03), while the dry-mass elemental concentrations in the two granule fractions were unchanged. These results indicate that protein is added to granules during the maturation process (presumably by vesicular traffic), and that the resulting increase in granule density is not driven simply by decrease in water content and/or increased concentrations of inorganic Ca or S in the granules. The elemental concentration values also indicate that the diffusible elements permeate the granule membrane during the fractionation procedures.     

Duplications of the X chromosome in males: evidence that most parts of the X chromosome can be active in two copies

Summary We have analysed two duplications of the X chromosome in male patients using chromosome replication and DNA methylation patterns as determinants of the functional status of the duplicated segments. In both cases, the large duplicated regions, Xq12-q22 and Xq26.3-qter, were not inactivated. A review of previously reported male cases revealed that these duplications were also not subject to inactivation. Taken together, the examined duplications cover almost the entire X chromosome except the pericentromeric region and Xq25–26. Thus, most regions of the X chromosome can be present in two functional copies without lethal consequences.