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B Gu

Publications and source records attributed to B Gu.

At least 55 records · Page 3Linked to original sources
PubMed1994

The role of ICP4 repressor activity in temporal expression of the IE-3 and latency-associated transcript promoters during HSV-1 infection.

The herpes simplex virus (HSV) type 1 immediate-early protein ICP4 represses transcription of its own gene and possibly that of other immediate-early genes. In the present study, we analyzed the role that an ICP4 binding site present in two HSV-1 promoters plays in the level and kinetics of expression during HSV-1 infection. Wild-type and mutant forms of the IE-3 (ICP4) promoter and the latency associated promoter (LAP) were fused to the thymidine kinase (tk) coding sequences and transferred to the genome of an ICP4-deficient virus. Promoter mutants were constructed to assess the effect of the ICP4 binding site in the presence and absence of defined binding sites for cellular and other viral factors in the promoters. The activities of the promoter constructs were inferred from the level of tk mRNA seen following viral infection in the absence of ICP4, in Vero cells and in the presence of ICP4 in ICP4 expressing E5 cells. Kinetics of expression and the dependence on DNA synthesis for expression were examined following infection of E5 cells. In the presence of the ICP4 binding site in LAP and in IE3 promoters lacking TAATGARAT motifs, expression was maximal late after infection and was greatly reduced when DNA synthesis was inhibited. When the ICP4 binding site was removed, both LAP and the IE3 construct retaining an Sp1 site were more abundantly expressed and exhibited kinetics of expression indistinguishable from that of the tk promoter. In vitro, ICP4 repressed LAP transcription mediated by the general transcription factors and upstream activating proteins. Deletion of the ICP4 binding site not only relieved repression, but in the presence of USF activity, ICP4 further induced LAP transcription. The results of these experiments suggest a role for the repressor activity of ICP4 in the temporal regulation of HSV-1 transcription.

Animals↗
PubMed1994

Rhizobium meliloti DctD, a sigma 54-dependent transcriptional activator, may be negatively controlled by a subdomain in the C-terminal end of its two-component receiver module.

Rhizobium meliloti DctD is believed to have three functional domains: an N-terminal, two-component receiver domain; and like other sigma 54-dependent activators, C-terminal and central domains for DNA binding and transcription activation. We have characterized a progressive series of N-terminal deletions of R. meliloti DctD. The N-terminal domain was not needed for binding the dctA upstream activation sequence. Only 25% of the C-terminal end of the receive domain was needed to significantly inhibit the central domain, and proteins lacking up to 60% of the N-terminal end of the receiver domain were 'inducible' in R. meliloti cells. We hypothesize that the N-terminal two-thirds of the DctD receiver domain augments and controls an adjacent subdomain for inhibiting the central domain.

Bacterial Proteins↗
PubMed1994

Requirements for activation of the herpes simplex virus glycoprotein C promoter in vitro by the viral regulatory protein ICP4.

During infection with herpes simplex virus, infected-cell polypeptide 4 (ICP4) activates transcription of most herpes simplex virus genes. In the present study, the mechanism of activation of transcription by ICP4 was investigated by using a reconstituted in vitro system with fractionated and purified general transcription factors, coupled with DNA-binding assays. The templates used in the reactions included regions of the gC and thymidine kinase (tk) promoters in plasmids, and on isolated fragments, allowing for the evaluation of the potential function of naturally occurring and inserted ICP4-binding sites and elements of the core promoter. ICP4 efficiently activated transcription of the gC promoter by facilitating the formation of transcription initiation complexes. ICP4 could not substitute for any of the basal transcription factors. Moreover, TATA-binding protein (TBP) could not substitute for TFIID in activation, suggesting a requirement for TBP-associated factors. Interactions between ICP4 and DNA 3' to the start site was necessary for activation of the gC promoter. The requirement for DNA-protein contacts could be met either by the presence of an ICP4-binding site in the gC leader, by the presence of a site more than 150 nucleotides further downstream, by an inserted site that normally acts to repress transcription, or by the addition of sufficient non-site-containing DNA. The gC TATA box and start site, or initiator element (inr), were individually sufficient for activation by ICP4 and together contributed to optimal activation. In contrast to gC, the tk promoter was poorly activated in the reconstituted system. However, the tk TATA box was efficiently activated when the tk start site region was replaced with the gC inr, suggesting that activation was mediated through the inr and inr-binding proteins. In addition, mutation of the inr core resulted in a gC promoter that was very poorly activated by ICP4. The results of this and previous studies demonstrate that ICP4 activates transcription in a complex manner involving contacts with DNA 3' to the start site, TBP, TFIIB, TBP-associated factors, and possibly proteins functioning at the start site of transcription.

Base Sequence↗
PubMed1993

Herpes simplex virus infected cell polypeptide 4 preferentially represses Sp1-activated over basal transcription from its own promoter.

Herpes simplex virus type 1 infected cell polypeptide 4 (HSV-1 ICP4) is a multifunctional phosphoprotein that is essential for viral infection. It is both a repressor and an activator of viral gene expression depending upon the promoter. ICP4 represses transcription from its own promoter. In the present study, we used general transcription factors from HeLa cell nuclear extracts, recombinant TATA binding protein (TBP) and TFIIB, and the transcriptional activator Sp1 to reconstitute in vitro transcription for the ICP4 promoter and to examine the effects of purified ICP4 on transcription. ICP4 was able to effectively repress Sp1-induced transcription from ICP4 promoter templates that contain one or multiple Sp1 binding sites. The observed inhibition required the ICP4 binding site that spans the transcription initiation site. ICP4 did not inhibit basal transcription as inferred by its inability to inhibit transcription when (i) Sp1 was not included in transcription reactions, (ii) the templates contained no Sp1 binding sites, and (iii) TBP was used in place of TFIID in the reactions. The in vitro observations were consistent with the behavior of the same constructs expressed in cells from the herpes simplex virus type 1 genome. DNase I footprinting experiments revealed that ICP4 could co-occupy the ICP4 promoter region with TBP-TFIIB, indicating that ICP4 does not necessarily exclude these factors from binding to the TATA region. The data suggest that the repressive effects of ICP4 observed in this study result from ICP4 interfering with the interactions contributing to Sp1-induced transcription.

Base Sequence↗
PubMed1993

Dissolved Nitrogen Uptake by a Cyanobacterial Bloom (Anabaena flos-aquae) in a Subarctic Lake.

Uptake of dissolved nitrogen (NH(4) + NO(3) + urea + N(2)) by a cyanobacterial [Anabaena flos-aquae (Lyngb.)] De Brèb population in Smith Lake, Alaska, was measured every 2 to 4 days during the spring of 1990. Total dissolved nitrogen uptake ranged from 0.34 to 24.75 mumol liter h, with a mean of 5.75 mumol liter h; the euphotic zone accounted for 91% of the uptake. The mean turnover time for dissolved combined nitrogen (NH(4) + NO(3) + urea) in the euphotic zone was less than 14 h, and that for NH(4) was only 3.6 h. The mean relative preference indices for NH(4) (2.4), NO(3) (0.4), and urea (0.5) established NH(4) as the preferred nitrogenous nutrient. The uptake rates were apparently dependent on biomass, temperature, and light. Regeneration, probably due to zooplankton excretion and bacterial remineralization of dissolved organic nitrogen, was the main source of NH(4) for the cyanobacterial growth. The high half-saturation constant for NH(4) with low ambient NH(4) concentration nevertheless resulted in the simultaneous utilization of several forms of nitrogen.

Journal Article↗
PubMed1993

ICP4, the major transcriptional regulatory protein of herpes simplex virus type 1, forms a tripartite complex with TATA-binding protein and TFIIB.

The ICP4 protein of herpes simplex virus can either increase or decrease the rate of transcription mediated by RNA polymerase II, depending on the target promoter. The interplay of DNA-protein and protein-protein contacts determining ICP4 function has yet to be characterized, and consequently the molecular mechanism by which the protein acts remains unclear. ICP4 can transactivate minimal promoters containing only TATA homologies, and therefore it is reasonable to hypothesize that ICP4 works by influencing the TATA-dependent assembly of general transcription factors via specific protein-protein interactions. This study directly addresses this hypothesis by determining whether ICP4 affects the assembly of general transcription factors on templates bearing a TATA box and an ICP4-binding site. Using gel retardation and footprinting assays, we found that ICP4 forms a tripartite complex with TFIIB and either the TATA-binding protein (TBP) or TFIID. The formation of this complex was not the result of simple tripartite occupancy of the DNA but the consequence of protein-protein interactions. In the presence of all three proteins, the affinity of ICP4 and TBP for their respective binding sites was substantially increased. Using mutant derivatives of ICP4 and defective versions of promoters, we also demonstrated that the ability of ICP4 to regulate gene expression correlated with its ability to form a tripartite complex with TFIIB and TBP in vitro.

Animals↗
PubMed1993

Relationship between the characteristics of immunopathological expression of hepatitis C virus antigen and hepatocytic injury.

Biopsied liver tissues from 352 cases were tested for hepatitis C virus (HCVAg) with improved PAP immunohistologic chemical method. Furthermore, corresponding seroantibody to hepatitis C virus was also tested. The total HCVAg positive rate was 9.1%. The HCVAg positive rate in chronic persistent hepatitis (CPH) was 5%. The HCVAg positive rate in chronic active hepatitis (CAH) was 11.2%. The HCVAg positive rate raised gradually along with the severity of hepatocytic injury. HCVAg may be seen in necrotic liver cells exfoliating into the liver sinus, indicating a close relationship between HCVAg and hepatocytic injury. Expression of HCVAg was mostly of the nucleus type in CPH cases and was mostly of the plasma type in CAH cases. The periphery of nucleus type-expressed positive cells generally had no marked inflammatory cell infiltration. The periphery of plasma type-expressed positive cells had a certain amount of inflammatory cell infiltration. Along with the severity of hepatocytic injury, HCVAg expressed itself in a positive correlation according to the nucleus and plasma types. The HCVAg positive cells were located mostly in the lobular peripheral band and rarely located in the venoperipheral band. It was possible that this had some relation with the lobular microcirculation of blood and blood supply. In this study, there was no obvious correlation between the HCVAg positive rate in hepatic tissues and the anti-HCV positive rate in sera. Neither the patients with HCVAg positive liver tissues nor the patients with seropositive anti-HCV had any history of blood transfusion and the use of blood products.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗