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151.
Cyanophages infecting marine Synechococcus cells were frequently very abundant and were found in every seawater sample along a transect in the western Gulf of Mexico and during a 28-month period in Aransas Pass, Tex. In Aransas Pass their abundance varied seasonally, with the lowest concentrations coincident with cooler water and lower salinity. Along the transect, viruses infecting Synechococcus strains DC2 and SYN48 ranged in concentration from a few hundred per milliliter at 97 m deep and 83 km offshore to ca. 4 x 10 ml near the surface at stations within 18 km of the coast. The highest concentrations occurred at the surface, where salinity decreased from ca. 35.5 to 34 ppt and Synechococcus concentrations were greatest. Viruses infecting strains SNC1, SNC2, and 838BG were distributed in a similar manner but were much less abundant (<10 to >5 x 10 ml). When Synechococcus concentrations exceeded ca. 10 ml, cyanophage concentrations increased markedly (ca. 10 to > 10 ml), suggesting that a minimum host density was required for efficient viral propagation. Data on the decay rate of viral infectivity d (per day), as a function of solar irradiance I (millimoles of quanta per square meter per second), were used to develop a relationship (d = 0.2610I - 0.00718; r = 0.69) for conservatively estimating the destruction of infectious viruses in the mixed layer of two offshore stations. Assuming that virus production balances losses and that the burst size is 250, ca. 5 to 7% of Synechococcus cells would be infected daily by viruses. Calculations based on contact rates between Synechococcus cells and infectious viruses produce similar results (5 to 14%). Moreover, balancing estimates of viral production with contact rates for the farthest offshore station required that most Synechococcus cells be susceptible to infection, that most contacts result in infection, and that the burst size be about 324 viruses per lytic event. In contrast, in nearshore waters, where ca. 80% of Synechococcus cells would be contacted daily by infectious cyanophages, only ca. 1% of the contacts would have to result in infection to balance the estimated virus removal rates. These results indicate that cyanophages are an abundant and dynamic component of marine planktonic communities and are probably responsible for lysing a small but significant portion of the Synechococcus population on a daily basis. 相似文献
152.
The contiguous trbJ and trbK genes of RP1 were cloned individually to study their effects. Surface exclusion was conferred only by trbK and only when gene dosage was high or when trbJ was also present in cis or in trans. This suggests that in the low-copy-number RP1, surface exclusion is due to a two-gene interaction in which trbK is the dominant partner. Among surface exclusion genes, trbJ is novel in yielding a periplasmic product that is also essential for conjugal transfer. This cellular location and the disturbed membrane function that accompanies TrbJ-processing probably accounts for the retarded growth caused by trbJ+ clones in Pseudomonas aeruginosa strain PAO. 相似文献
153.
Julie Y. H. Chan Hsing-Fei Tsai Terry B. J. Kuo Samuel H. H. Chan 《Regulatory peptides》1994,50(3):247-257
We evaluated possible modulation by angiotensin III (AIII) of the interactive effect of noxious stimuli and elevation in systemic arterial pressure on the responsiveness of neurons in the nucleus reticularis gigantocellularis (NRGC) of the medulla oblongata. Combined extracellular single-neuron recording and microiontophoresis were carried out on male, adult Sprague-Dawley rats anesthetized with pentobarbital sodium. The responsiveness of NRGC neurons to nociception (tail clamp) and/or transient hypertension elicited by phenylephrine (5 μg/kg, i.v.), in the absence or presence of AIII, was used as the experimental index. Microiontophoretic application of the heptapeptide suppressed the responses of spontaneously active NRGC neurons to individually delivered nociception or hypertension. Interestingly, the preferential reduction in responsiveness to tail clamp upon simultaneous elevation in arterial pressure was reversed to one that favored nociception in the presence of AIII. These actions of the heptapeptide appeared to be receptor-specific, since they were discernibly blocked by its selective antagonist, Ile7-angiotensin III. Our results reveal that neuropeptides such as AIII may differentially modulate neuronal responsiveness according to the prevailing physiologic input(s) to the central nervous system of the animal. 相似文献
154.
Alexander N. Glazer Yvonne M. Gindt Crystal F. Chan Kenneth Sauer 《Photosynthesis research》1994,40(2):167-173
Efficient production of ATP and NADPH by the light reactions of oxygen-evolving photosynthesis demands continuous adjustment of transfer of absorbed light energy from antenna complexes to Photosystem I (PS I) and II (PS II) reaction center complexes in response to changes in light quality. Treatment of intact cyanobacterial cells with N-ethylmaleimide appears to disrupt energy transfer from phycobilisomes to Photosystem I (PS I). Energy transfer from phycobilisomes to Photosystem II (PS II) is unperturbed. Spectroscopic analysis indicates that the individual complexes (phycobilisomes, PS II, PS I) remain functionally intact under these conditions. The results are consistent with the presence of connections between phycobiliproteins and both PS II and PS I, but they do not support the existence of direct contacts between the two photosystems.Abbreviations Chl
chlorophyll
- EPR
electron paramagnetic resonance
- NEM
N-ethylmaleimide
- PBS
phycobilisome
- PS
photosystem 相似文献
155.
Ann-ping Tsou Alan Kosaka Chinh Bach Patti Zuppan Calvin Yee Leonard Tom Robert Alvarez Scott Ramsey Douglas W. Bonhaus Eric Stefanich Lyn Jakeman Richard M. Eglen Hardy W. Chan 《Journal of neurochemistry》1994,63(2):456-464
Abstract: In a number of different cell types, phosphorylation of a 63-kDa protein has been shown to increase rapidly in response to stimuli that lead to an increase in intracellular calcium. Here, a stimulus-sensitive protein at this molecular weight is identified in PC12 cells and rat cortical synaptosomes as phosphoglucomutase. In addition, the added phosphate is shown to be in an oligosaccharide terminating in phosphodiester-linked glucose. In synaptosomes, incorporated radioactivity, following incubation with [14 C]glucose or the [β-35 S]phosphorothioate analogue of UDP-glucose, was found to increase within 5 s of stimulation and return to baseline within 25 s. Despite the many pathways utilizing glucose, this was the only detectable protein glycosylation observed in synaptosomes. These results indicate that cytoplasmic glycosylation is reversible and rapidly regulated, and suggest that phosphoglucomutase undergoes an alteration in function and/or topography in response to increases in intracellular calcium. 相似文献
156.
Cloning of the nupC gene of Escherichia coli encoding a nucleoside transport system, and identification of an adjacent Insertion element, IS 186 总被引:1,自引:0,他引:1
Escherichia coli is known to contain more than one active transport system for nucleoside uptake. In the present study we report the sequence of a gene encoding a second nucleoside transport system, nupC (in addition to nupG.) An open reading frame (ORF) of 1200bp was identified that codes for a hydrophobic polypeptide of 43 560 Da and an NupC fusion protein was shown to be membrane associated. The native NupC protein is also identified, following over-expression. NupC exhibits short regions of homology to several membrane-associated proteins, including LacY and Cyd. Analysis of the nupC promoter region revealed the presence of at least two putative CRP-binding sites, centred at–40bp and–89bp, which probably flank a CytR-binding site. In addition, an adjacent IS186 element was identified and found to reside within a putative terminator structure, downstream from the nupC ORF. This arrangement is shown to reflect the previously established gene order on the E. coli chromosome. 相似文献
157.
Structural and functional diversity among bacterial interspersed mosaic elements (BIMEs) 总被引:7,自引:0,他引:7
Sophie Bachellier William Saurin David Perrin Maurice Hofnung Eric Gilson† 《Molecular microbiology》1994,12(1):61-70
Palindromic units (PU or REP) were defined as 40-nucleotide DNA sequences which are highly repeated in the genome of several members of the Enterobacteriaceae. They were shown to be a constituent of the bacterial interspersed mosaic element (BIME), in which they are associated with other repetitive sequences. We report here that Escherichia coli PU sequences contain three motifs (Y, Z1 and Z2), leading to the definition of two BIME families. The BIME-1 family, highly conserved over 145 nucleotides, contains two PUs (motifs Y and Z1). The BIME-2 family contains a variable number of PUs (motifs Y and Z2). We present evidence, using band shift experiments, that each PU motif binds DNA gyrase with a different affinity. This suggests that the two families are functionally distinct. 相似文献
158.
Ho-Yin Chan Ying-Chi Chan Kai-Man Kam Pang-Chui Shaw 《World journal of microbiology & biotechnology》1994,10(1):30-32
An Enterobacter cloacae strain, producing restriction enzyme EclHKI, was isolated from a decaying potato. The enzyme is an isoschizomer of Eam1105I, which recognizes and cleaves GACNNN!NNGTC. EclHKI was produced at high activity (4×104 U/g wet cells) and was purified from contaminants which interfere with restriction digestion by passing the cell lysate through DEAE-Sephacel and heparin columns. Activity was optimal at 37°C in a medium salt buffer.H.-Y. Chan, Y.-C. Chan and P.-C. Shaw are with the Department of Biochemistry, The Chinese University of Hong Kong, Hong Kong: K.-M. Kam is with the Institute of Pathology, Sai Ying Pun Jockey Club Clinic, Hong Kong. 相似文献
159.
Astrocytes are important in regulating the microencironment of neurons both by catabolic and synthetic pathways. The glutamine synthetase (GS) activity observed in astrocytes affects neurons by removing toxic substances, NH3 and glutamate; and by providing an important neuronal substrate, glutamine. This glutamate cycle might play a critical role during periods of hypoxia and ischemia, when an increase in extracellular excitatory amino acids is observed. It was previously shown in our laboratory that fructose-1,6-bisphosphate (FBP) protected cortical astrocyte cultures from hypoxic insult and reduced ATP loss following a prolonged (18–30 hrs) hypoxia. In the present study we established the effects of FBP on the level of glutamate uptake and GS activity under normoxic and hypoxic conditions. Under normoxic conditions, [U-14C]glutamate uptake and glutamine production were independent of FBP treatment; whereas under hypoxic conditions, the initial increase in glutamate uptake and an overall increase in glutamine production in astrocytes were FBP-dependent. Glutamine synthetase activity was dependent on FBP added during the 22 hours of either normoxic- or hypoxic-treatment, hence significant increases in activity were observed due to FBP regardless of the oxygen/ATP levels in situ. These studies suggest that activation of GS by FBP may provide astrocytic protection against hypoxic injury. 相似文献
160.
Chong CF Ngoh BL Tan HC Yap EH Singh M Chan L Chan YC 《Clinical and diagnostic virology》1994,1(5-6):335-341
A shortened IgM capture ELISA for the detection of dengue IgM antibodies using simultaneous incubation of antigen and peroxidase-labeled monoclonal antibody was described. The shortened two-step assay was compared with the four-step IgM capture ELISA on sera from dengue patients confirmed by the hemagglutination inhibition (HI) test. When paired acute and convalescent sera were tested, the shortened ELISA showed 100% agreement with HI results. It detected dengue IgM antibodies in the acute sera of 66% of patients with a primary dengue infection, 60% of patients with a secondary infection, and 98% of patients with a presumptive secondary infection. When the results of 151 dengue patients were combined, 75% of the acute sera were positive by the shortened IgM capture ELISA. 相似文献