Sequence and functional analysis of the cloned Neisseria meningitidis CMP-NeuNAc synthetase

The CMP-N-acetylneuraminic acid (CMP-NeuNAc) synthetase gene of Neisseria meningitidis group B is located on a 2.3-kb EcoRI fragment within the cps gene cluster. Nucleotide sequence determination of the gene encoding the CMP-NeuNAc synthetase revealed a 515-bp open reading frame that can encode a 18.9-kDA protein. A computer data base scan revealed a 59.4% identity to the CMP-NeuNAc synthetase gene of E. coli K1. Enzymatic activity was confirmed in vitro and in vivo. Transformation of the CMP-NeuNAc defective E. coli K1 strain EV5 with the meningococcal CMP-NeuNAc synthetase could complement the defect in E. coli.     

Targeting of porin to the outer membrane of Escherichia coli. Rate of trimer assembly and identification of a dimer intermediate

Porin, a transmembrane protein in the outer membrane of Escherichia coli, exists in a trimeric structure which is not dissociated during sodium dodecyl sulfate-polyacrylamide gel electrophoresis at 25 degrees C. This unusual stability was utilized in the study of the conformational changes which accompany the targeting of porin to the outer membrane. A delay of 16-44 s between completion of synthesis of a monomer and its assembly into a trimer was found from the ratio of monomers to trimers found in exponentially growing cells. Pulse-chase experiments showed that rapid processing of precursor OmpF molecules was followed by assembly into sodium dodecyl sulfate-resistant oligomers with a half-time of 20 s at 30 degrees C. An intermediate in assembly was isolated by immunoprecipitation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis below 10 degrees C and was identified as a metastable dimer.     

The Effect of Traffic Density on Lead Contents in Roadside Soils: An Analysis of Published Data

Data from eight published studies were combined to show that the influence of traffic density on Pb contents in roadside soils increases with proximity to the road.     

In Situ and in Vitro Binding of Natriuretic Peptide Hormones in Tradescantia multiflora

Abstract: An increasing body of evidence suggests that in plants, as in vertebrates, biologically active natriuretic peptide (NP) hormones play an important role in the regulation of the osmotic and ionic balance. The evidence includes isolation and immunoaffinity purification of biologically active natriuretic peptide analogues (irPNP) from ivy that promoted stomatal opening and specifically, rapidly and transiently increased cGMP levels in root conductive tissue. In this study we demonstrate that I¹²⁵-rat atrial natriuretic peptide (rANP) binds to plasma membranes from leaf and stem tissue of Tradescantia multiflora and importantly, both unlabelled rANP and irPNP can competitively displace that binding. In addition, tissue section autoradiography reveals specific in situ binding of I¹²⁵-rANP to leaf and stem tissue. The findings are consistent with the presence of a biologically active NP system in plants and suggest that NPs signal through a dedicated receptor system.     

Regulation and function of the Drosophila segmentation gene fushi tarazu

The Drosophila segmentation gene fushi tarazu (ftz) is expressed in a pattern of seven stripes at the blastoderm stage. Two cis-acting control elements are required for this expression: the zebra element, which confers the striped pattern by mediating the effects of a subset of segmentation genes; and the upstream element, an enhancer element requiring ftz+ activity for its action. Fusion of the upstream element to a basal promoter results in activation of the heterologous promoter in a ftz-dependent striped pattern, supporting the idea that ftz regulates itself by acting through its enhancer. The upstream element can also confer expression patterns similar to that of the homeotic gene Antennapedia, suggesting that a similar element may play a role in the activation of Antennapedia.     

Retardation of cell cycle progression in yeast cells recovering from DNA damage: A study at the single cell level

Summary Pedigree analyses of individual yeast cells recovering from DNA damage were performed and time intervals between morphological landmark events during the cell cycle (bud emergence and cell separation), were recorded for three generations. The associated nuclear behavior was monitored with the aid of DAPI staining. The following observations were made: (1) All agents tested (X-rays, MMS, EMS, MNNG, nitrous acid) delayed the first bud emergence after treatment, which indicates inhibition of the initiation of DNA replication. (2) Cells that survived X-irradiation progressed further through the cell cycle in a similar way to control cells. (3) Progress of chemically treated cells became extremely asynchronous because surviving cells stayed undivided for periods of varying length. (4) Prolongation of the time between bud emergence and cell separation was most pronounced for cells treated with the alkylating agents MMS and EMS. This is interpreted as retardation of ongoing DNA synthesis by persisting DNA adducts. (5) Cell cycle prolongation in the second and third generation after treatment was observed only with MMS treated cells. (6) In all experiments, individual cells of uniformly treated populations exhibited highly variable responses.Abbreviations DAPI 4,6-diamidino-2-phenyl-indole - EMS ethyl methanesulfonate - MMS methyl methanesulfonate - MNNG N-methyl-N-nitro-N-nitrosoguanidine     

The accumulation of mature RNA for the Xenopus laevis ribosomal protein L1 is controlled at the level of splicing and turnover of the precursor RNA.

A specific control regulates, at the level of RNA splicing, the expression of the L1 ribosomal protein gene in Xenopus laevis. Under particular conditions, which can be summarized as an excess of free L1 protein, a precursor RNA which still contains two of the nine introns of the L1 gene accumulates. In addition to the splicing block the two intron regions undergo specific endonucleolytic cleavages which produce abortive truncated molecules. The accumulation of mature L1 RNA therefore results from the regulation of the nuclear stability of its precursor RNA. We propose that a block to splicing can permit the attack of specific intron regions by nucleases which destabilize the pre-mRNA in the nucleus. Therefore the efficiency of splicing could indirectly control the stability of the pre-mRNA.