Herpes simplex virus immediate-early protein ICP22 is required for viral modification of host RNA polymerase II and establishment of the normal viral transcription program

Infection of cells with herpes simplex virus type 1 (HSV-1) results in a rapid alteration of phosphorylation on the large subunit of cellular RNA polymerase II (RNAP II), most likely on its C-terminal domain (S. A. Rice, M. C. Long, V. Lam, C. A. Spencer, J. Virol. 68:988-1001, 1994). This phosphorylation modification generates a novel form of the large subunit which we have designed IIi. In this study, we examine roles that HSV-1 gene products play in this process. An HSV-1 mutant defective in the immediate-early transcriptional activator protein ICP4 is able to efficiently induce IIi. Viruses having mutations in the genes for the ICP0, ICP6, or ICP27 proteins are also competent for IIi formation. In contrast, 22/n199, an HSV-1 mutant which contains a nonsense mutation in the gene encoding the immediate-early protein ICP22, is significantly deficient in IIi induction. This effect is seen in Vero cells, where 22/n199 grows relatively efficiently, and in human embryonic lung (HEL) cells, where 22/n199 growth in more restricted. RNAP II is recruited into viral replication compartments in 22/n199-infected cells, indicating that altered phosphorylation of RNAP II is not a prerequisite for nuclear relocalization of RNAP II. In addition, we show by nuclear run-on transcription analysis that viral gene transcription is deficient in HEL cells infected with 22/n199. Viral late gene transcription does not occur efficiently, and antisense transcription throughout the genome is diminished compared with that of the wild-type HSV-1 infection. These transcriptional effects cannot be explained by differences in viral DNA replication, since 22/n199 replicates its DNA efficiently in HEL cells. Our results demonstrated that ICP22 is necessary for virus-induced aberrant phosphorylation of RNAP II and for normal patterns of viral gene transcription in certain cell lines.

Bacterial reverse transcriptase and msDNA

Retrons are a new class of genetic elements found in the chromosome of a large number of different bacteria. These elements code for a reverse transcriptase (RT) that is structurally similar to the polymerases of retroviruses. The retron associated RT is responsible for the production of an unusual extrachromosomal satellite DNA, known as multicopy, single-stranded DNA (msDNA). Synthesis of msDNA is dependent on a novel self-priming mechanism, resulting in the formation of a 2',5'-phosphodiester bond. A comparison of bacterial RTs is presented, noting conserved and unique features of these polymerases. In addition, the origin, means of dissemination, and possible activities of these functionally obscure retroelements are discussed.

Identification of nuclear and nucleolar localization signals in the herpes simplex virus regulatory protein ICP27

Previous work has shown that the herpes simplex virus type 1 (HSV-1) regulatory protein ICP27 localizes to the cell nucleus and that certain mutant ICP27 polypeptides localize preferentially in nucleoli. To map the signals in ICP27 which mediate its nuclear localization, we identified the portions of ICP27 which can direct a cytoplasmic protein, pyruvate kinase (PK), to nuclei. Our results demonstrate that ICP27 contains multiple nuclear localization signals (NLSs) that function with differing efficiencies. First, ICP27 possesses a strong NLS, mapping to residues 110 to 137, which bears similarity to the bipartite NLSs found in Xenopus laevis nucleoplasmin and other proteins. Second, ICP27 possesses one or more weak NLSs which map to a carboxyl-terminal portion of the protein between residues 140 and 512. Our PK-targeting experiments also demonstrate that ICP27 contains a relatively short sequence, mapping to residues 110 to 152, that can function as a nucleolar localization signal (NuLS). This signal includes ICP27's strong NLS as well as 15 contiguous residues which consist entirely of arginine and glycine. This latter sequence is very similar to an RGG box, a putative RNA-binding motif found in a number of cellular proteins which are involved in nuclear RNA processing. To confirm the results of the PK-targeting experiments, we mutated the ICP27 gene by deleting sequences encoding either the strong NLS or the RGG box. Deletion of the strong NLS (residues 109 to 138) resulted in an ICP27 molecule that was only partially defective for nuclear localization, while deletion of the RGG box (residues 139 to 153) resulted in a molecule that was nuclear localized but excluded from nucleoli. Recombinant HSV-1s bearing either of these deletions were unable to replicate efficiently in Vero cells, suggesting that ICP27's strong NLS and RGG box carry out important in vivo functions.

Phylogenetic comparison of retron elements among the myxobacteria: evidence for vertical inheritance

Twenty-eight myxobacterial strains, representing members from all three subgroups, were screened for the presence of retron elements, which are novel prokaryotic retroelements encoding reverse transcriptase. The presence of retrons was determined by assaying strains for a small satellite DNA produced by reverse transcription called multicopy, single-stranded DNA (msDNA). An msDNA-producing retron appeared to be absent from only one of the strains surveyed. DNA hybridization experiments revealed that retron elements similar to retron Mx162, first identified in Myxococcus xanthus, were found only among members of the Myxococcus subgroup; that is, each of the seven different genera which constitute this subgroup contained a Mx162 homolog. Another retron element also appeared to have a clustered distribution, being found exclusively within the Nannocystis subgroup of the myxobacteria. A retron element of the Mx162 type was cloned from Melittangium lichenicola, and its DNA sequence was compared with those of similar elements in M. xanthus and Stigmatella aurantiaca. Together, the degree of sequence diversity, the codon bias of the reverse transcriptase genes, and the clustered distribution of these retrons suggest a possible evolutionary scenario in which a common ancestor of the Myxococcus subgroup may have acquired this retroelement.

A poxvirus protein with a RING finger motif binds zinc and localizes in virus factories

Shope fibroma virus (SFV) is a Leporipoxvirus closely related to the highly virulent myxoma virus. The DNA sequence of the BamHI N fragment of the SFV DNA genome was determined, and the single complete open reading frame (N1R) was characterized. The protein encoded by the N1R gene was found to contain a C3HC4 RING finger motif at the C terminus. This C3HC4 motif is the hallmark of a growing family of proteins, many of which are involved in regulation of gene expression, DNA repair, or DNA recombination. Complete homologs of the SFV N1R gene were also detected in variola virus, myxoma virus, and vaccinia virus strain IHD-W. In contrast, the gene is completely absent from vaccinia virus strain Copenhagen, and in vaccinia virus strain WR, the open reading frame is truncated prior to the zinc binding domain because of an 11-bp deletion, thus producing a frameshift and premature stop codon. Recombinant N1R protein from SFV was expressed in Escherichia coli and shown to bind zinc in a specific manner. Using fluorescence microscopy to visualize a peptide epitope tag (derived from ICP27 of herpes simplex virus) fused to the N terminus of the poxvirus proteins, we observed that the N1R protein of SFV and its homologs in myxoma virus and vaccinia virus IHD-W were localized primarily to the virus factories in the cytoplasm of infected cells and, to a lesser degree, the host cell nucleus. The truncated protein of vaccinia virus strain WR failed to localize in this manner but instead was observed throughout the cytoplasm.

UL69 of human cytomegalovirus, an open reading frame with homology to ICP27 of herpes simplex virus, encodes a transactivator of gene expression

The UL69 open reading frame of human cytomegalovirus (HCMV) is homologous to the immediate-early protein ICP27 of herpes simplex virus, an essential viral regulatory protein involved in the transition from early to late gene expression. Genes with homology to ICP27 have been detected in all subclasses of herpesviruses so far. While the respective proteins in alpha- and gammaherpesviruses have been defined as trans-regulatory molecules, nothing is known about these genes in betaherpesviruses. This study was therefore undertaken in order to investigate expression from the UL69 gene locus of HCMV. Northern (RNA) blot experiments revealed a complex pattern of transcripts that changed during the time course of the HCMV replicative cycle: two transcripts of 2.7 and 3.5 kb that were regulated differentially could be detected as early as 7 h after infection. However, these transcripts could not be detected in the presence of cycloheximide. Additional, larger transcripts were present exclusively at late times after infection. To analyze protein expression from the UL69 gene region, the UL69 open reading frame was expressed as a histidine-tagged protein in Escherichia coli. A specific antiserum was generated and used to detect the UL69 protein in HCMV-infected cells which revealed its localization within the intranuclear inclusions that are characteristic for HCMV infection. In cotransfection experiments, an HCMV true late promoter could not be activated by UL69, whereas an early promoter and several heterologous promoters were stimulated about 10-fold. Complementation studies showed that the UL69 protein cannot substitute for ICP27 in the context of the HSV infection, suggesting functional differences between these two proteins. In summary, these experiments define a novel regulatory protein encoded by HCMV that is expressed as an early-late gene and appears to exert a broad stimulatory effect on gene expression.

Amino acid substitution mutations in the herpes simplex virus ICP27 protein define an essential gene regulation function

ICP27 is an essential herpes simplex virus type 1 (HSV-1) alpha protein that is required for the transition from the beta to the gamma phase of infection. To identify functional regions of ICP27, we constructed 16 plasmids that contain nucleotide substitution mutations in the ICP27 gene. The mutations created XhoI restriction sites, altered one or two codons, and were spaced at semiregular intervals throughout the coding region. Three mutations completely inactivated an essential function of ICP27, as demonstrated by the inability of the transfected plasmids to complement the growth of an HSV-1 ICP27 deletion mutant. These mutations, M11, M15, and M16, mapped in the carboxyl-terminal one-third of ICP27 at residues 340 and 341, 465 and 466, and 488, respectively. In cotransfection assays, all three defective-plasmid mutants retained the transrepression function of ICP27 but were defective at transactivation. To define the lytic functions that are mediated by the transactivation activity of ICP27, we engineered HSV-1 recombinants containing the M11, M15, or M16 mutation. All three viral mutants failed to grow in Vero cells and possessed similar phenotypes. The viral mutants replicated their DNA similarly to the wild-type virus but showed several defects in viral gene expression. These were a failure to down-regulate alpha and beta genes at late times after infection and an inability to induce certain gamma-2 genes. Our results demonstrate that the transactivation function of ICP27 (as it is defined in cotransfection assays) mediates an essential gene regulation function during the HSV-1 infection. This activity is not required for ICP27-dependent enhancement of viral DNA replication. Our work supports and extends previous studies which suggest that ICP27 carries out two distinct regulatory activities during the HSV-1 infection.

RNA polymerase II is aberrantly phosphorylated and localized to viral replication compartments following herpes simplex virus infection

During lytic infection, herpes simplex virus subverts the host cell RNA polymerase II transcription machinery to efficiently express its own genome while repressing the expression of most cellular genes. The mechanism by which RNA polymerase II is directed to the viral delayed-early and late genes is still unresolved. We report here that RNA polymerase II is preferentially localized to viral replication compartments early after infection with herpes simplex virus type 1. Concurrent with recruitment of RNA polymerase II into viral compartments is a rapid and aberrant phosphorylation of the large subunit carboxy-terminal domain (CTD). Aberrant phosphorylation of the CTD requires early viral gene expression but is not dependent on viral DNA replication or on the formation of viral replication compartments. Localization of RNA polymerase II and modifications to the CTD may be instrumental in favoring transcription of viral genes and repressing specific transcription of cellular genes.

Diversity of retron elements in a population of rhizobia and other gram-negative bacteria

Genetic elements called retrons reside on the chromosome of Escherichia coli and the myxobacteria and represent the first reverse transcriptase-encoding element to be found in a prokaryotic cell. All known retrons produce a functionally obscure RNA-DNA satellite molecule called multicopy single-stranded DNA (msDNA). We report here the presence of msDNA-producing retron elements in a number of new bacterial groups, including strains of the genera Proteus, Klebsiella, Salmonella, Nannocystis, Rhizobium, and Bradyrhizobium. Among a population of 63 rhizobia strains, only 16% contain a retron element. The rhizobia retrons appear to be heterogeneous in nucleotide sequence and show little similarity to previously studied retrons of E. coli and the myxobacteria.

The clinical spectrum of patients with aneurysms of the ascending aorta

Aneurysms of the ascending aorta are often unsuspected, yet they can quickly lead to death from aortic rupture or dissection. To examine the clinical spectrum of patients with aneurysms of the ascending aorta, we searched the University of California, San Francisco (USCF) Echocardiography Data Base for all patients with aneurysms of the ascending aorta (> or = 5.0 cm in diameter) seen over a 7-year period. The echocardiograms and clinical courses of these patients were then reviewed. We identified 15 patients with aneurysms of the ascending aorta: five had aneurysms > 7.0 cm in diameter, three had aneurysms 6.0 to 6.9 cm, and seven had aneurysms 5.0 to 5.9 cm in diameter. Among the five patients < 50 years of age, four had Marfan's syndrome, and among the 10 patients > or = 50 years of age, eight had evidence of atherosclerotic vascular disease. At presentation, 13 patients had nonspecific symptoms, and two were asymptomatic. Echocardiography demonstrated that 12 patients had at least mild aortic insufficiency and that five had aortic dissections. One of the seven patients who underwent surgical resection died of an intraoperative cardiac arrest, and two of the eight patients treated medically died within 1 week of presentation. We conclude that the clinical spectrum of patients with aneurysms of the ascending aorta is wide. Because these aneurysms are often unsuspected, physicians should have a low threshold for imaging the ascending aorta in patients with Marfan's syndrome or atherosclerotic vascular disease, particularly when aortic insufficiency is present.

In-Plane Structure of the Liquid-Vapor Interface of an Alloy: A Grazing Incidence X-ray Diffraction Study of Bismuth:Gallium

The liquid-vapor interface of a bismuth-gallium mixture (0.2 percent bismuth and 99.8 percent gallium) at 36 degrees C has been studied by grazing incidence x-ray diffraction. The data show, in agreement with thermodynamic arguments, that bismuth is heavily concentrated in the liquid-vapor interface. The x-ray diffraction data are interpreted with the assistance of a simple model that represents the interface as a partial monolayer of bismuth. This analysis leads to the conclusion that the bismuth concentration in the interface is about 80 percent, that there is no significant mixing of gallium and bismuth in the interface, and that the structure function of the interfacial bismuth is like that of supercooled bulk liquid bismuth.

The acidic amino-terminal region of herpes simplex virus type 1 alpha protein ICP27 is required for an essential lytic function

The herpes simplex virus type 1 (HSV-1) alpha protein ICP27 regulates the transition between the delayed-early and late phases of the viral infection. Previous genetic analyses have suggested that the important functional domains of ICP27 map to its carboxyl-terminal half. One striking feature of the primary sequence of ICP27, however, is an extremely acidic region near its amino terminus. To determine whether this region is required for ICP27 function, we deleted the sequences in the ICP27 gene which encode it (codons 12 through 63). In transient expression assays, the deletion mutant was unable to efficiently repress the expression of a cotransfected reporter gene or to efficiently complement the growth of d27-1, an HSV-1 ICP27 null mutant. These results suggested that the acidic region of ICP27 is involved in a regulatory function required for lytic growth. To test this possibility further, we introduced the mutant allele into the HSV-1 genome by marker transfer. Two independently derived isolates of the mutant virus, designated d1-2a and d1-2b, were recovered and analyzed. Both isolates were defective for growth in Vero cells, exhibiting a 100-fold reduction in virus yield compared with the wild-type infection. Vero cells infected with the d1-2 isolates showed a three- to eightfold reduction in viral DNA replication, a moderate reduction in the expression of viral gamma genes, and a delay in the repression of beta genes. The phenotype of the d1-2 isolates differs substantially from the phenotypes of previously isolated ICP27 mutants, which show much more severe defects in viral gene expression. Our results demonstrate that the amino-terminal half of ICP27 participates in its regulatory activities in both infected and transfected cells.

Prolonged administration of isoflurane to pediatric patients during mechanical ventilation

We undertook a prospective study of the effectiveness and potential toxicities of isoflurane sedation in pediatric patients undergoing mechanical ventilation who required large doses of opioids for sedation were considered eligible. Ten patients (ages 3 wk to 19 yr) received continuous isoflurane sedation for a mean duration of 131 minimum alveolar concentration (MAC)-hours (range 13-497 MAC-hours). The mean peak inorganic fluoride (F-) concentration was 11.0 microM, and the highest F- concentration was 26.1 microM after 441 MAC-hours. Only one patient had a measured F- concentration greater than 20 microM. No abnormalities were noted in serum creatinine or osmolality. Creatinine clearances were available for five patients who received a mean of 193 MAC-hours of isoflurane (range 33-497 MAC-hours), and only one patient had a persistent decrease from baseline of more than 20%. Five patients demonstrated an abstinence syndrome which consisted of nonpurposeful movements and extreme agitation. All of these patients had received at least 70 MAC-hours of isoflurane. Our experience indicates that isoflurane can effectively provide sedation to pediatric patients for prolonged periods without significant adverse effects on cardiovascular, hepatic, or renal function.

Starvation Response of the Marine Barophile CNPT-3

The psychrophilic marine barophile CNPT-3 underwent a starvation-survival response similar to that reported for the marine bacteria Ant-300, DW1, and S-14. The number of culturable cells increased initially and then decreased gradually over a 24-day starvation period, with corresponding decreases in total cell number and direct viability count. A significant reduction in cell size and biovolume accompanied these changes. Starved cells demonstrated a greater tendency to attach at the in situ pressure (400 atm; ca. 40.5 MPa) and temperature (5°C) than at 1 atm (ca. 101 kPa), and the extent of attachment increased with increasing duration of starvation. The membrane fatty acid profile of the marine barophile CNPT-3 was studied as the cells were subjected to starvation conditions. A 37.5% increase in saturated fatty acids was observed during the first 8 days of starvation, with a concomitant decrease in unsaturated fatty acids. There was also an increase in the amount of short-chain (<C 15:0 ) fatty acids.

Longitudinal distribution of pulmonary vascular resistance after endotoxin administration in sheep

BACKGROUND AND METHODS

Pulmonary hypertension may increase pulmonary capillary pressure and exacerbate pulmonary edema in acute respiratory failure. The effects of pulmonary hypertension on pulmonary capillary pressure depend on the longitudinal distribution of pulmonary vascular resistance. Since pulmonary hypertension occurs during acute respiratory failure, we hypothesized that acute respiratory failure may produce time-dependent changes in the longitudinal distribution of pulmonary vascular resistance. Therefore, we measured pulmonary capillary pressure and the longitudinal distribution of pulmonary vascular resistance in an animal model of acute respiratory failure. Escherichia coli endotoxin (2.5 to 5.0 micrograms/kg) was administered over a 1-hr period in eight anesthetized sheep. Pulmonary and systemic hemodynamics, including pulmonary artery occlusion pressure (PAOP), pulmonary capillary pressure, and the longitudinal distribution of pulmonary vascular resistance, were measured over the next 5 hrs. Pulmonary capillary pressure was estimated by analysis of the pressure decay following pulmonary artery balloon inflation.

RESULTS

Endotoxin administration resulted in sustained pulmonary hypertension for the subsequent 5 hrs of the study. Pulmonary capillary pressure was increased 7 mm Hg above baseline at 0.5 and 0.75 hrs during the infusion of endotoxin but returned to baseline values at 1.5 hrs. Despite sustained pulmonary hypertension, pulmonary capillary pressure remained at baseline values for the duration of the study. Similar to pulmonary capillary pressure, pulmonary venous (or postcapillary) resistance was increased approximately four-fold over baseline at 0.5 and 0.75 hrs after initiating endotoxin administration, but returned to baseline values by the end of endotoxin administration and remained at baseline values throughout the remainder of the study. In contrast, pulmonary arterial (or precapillary) resistance remained at values approximately three times baseline during the infusion and throughout the duration of the study.

CONCLUSIONS

In this experimental model of acute respiratory failure, the effects of endotoxin on the longitudinal distribution of pulmonary vascular resistance are time-dependent. If these data from animals can be extrapolated to humans, we speculate that the importance of pulmonary venoconstriction in exacerbating pulmonary edema may vary over time in patients with acute respiratory failure.

Effects of thiourea tolerance on plasma histamine, and lung vascular permeability

Adult male rats treated with a lethal edematogenic dose of thiourea (TU) (10.0 mg/kg, intraperitoneally) responded with significant elevations in plasma histamine, lung vascular permeability and 100% mortality over a subsequent 24-h period. When rats were pretreated with a small non-lethal dose of TU (0.5 mg/kg) and subsequently challenged with the lethal dose at 1, 4, 8, 16 and 32 days later, there was complete protection against death for at least 8 days and partial protection for an additional 24 days. This decrease in mortality correlated quite closely with reduced plasma histamine levels and diminished pulmonary vascular permeability. The results suggest that reduced exposure of the pulmonary vasculature to histamine may offer a partial explanation for tolerance to thiocarbamide compounds in the rat.

Effects of thiourea on pulmonary vascular permeability and on lung and plasma histamine levels in rats

The intraperitoneal administration of thiourea (TU) to mature male rats results in a significant increase in lung vascular permeability to Evans Blue dye (EBD). On the other hand, young, sexually immature rats are resistant to this effect. The increase in lung vascular permeability in response to TU in mature rats is associated with corresponding increases in lung and plasma histamine levels. The correlation of increases in lung and plasma histamine in response to TU is similar to that reported for ammonium salts which produce similar pulmonary edema.

Effect of prenatal N2O exposure on startle reflex reactivity

The teratogenic effect of N2O is of interest because thousands of pregnant women are exposed to this gaseous anesthetic each year. The effects of repeated N2O exposures were investigated for offspring of mice exposed to air or N2O (5%, 15%, or 35%) for 4 hours per day on days 6 through 15 of pregnancy. Ten litters per exposure group were studied. Exposures did not affect reproductive indices, survival, or physical milestones of development. Body weights showed significant exposure effects that could not be isolated to specific exposure groups; however, N2O-exposed mice tended to weigh more than air-exposed animals. Brain weights measured on postnatal day (PND) 126 or 127 were not different among exposure groups or between genders. Ability to stay on a rotating rod was not affected by prenatal N2O exposure. Prenatal exposure to N2O resulted in hyporeactivity of the startle reflex in response to acoustic or tactile stimuli. On PND 95 the results were statistically significant for all N2O-exposed groups compared with the air-exposed group. On PND 60, although not statistically significant, there was a definite trend toward hyporeactivity for the N2O groups. There was a significant age-related difference in startle response; control animals were significantly more reactive at 95 than at 60 days of age. Of the N2O-exposed groups, only the 15% group showed a statistically significant increase in reactivity from 60 to 95 days of age. The risk of behavioral or functional abnormalities for humans following in utero N2O exposure is unknown and cannot be directly extrapolated from the present study.(ABSTRACT TRUNCATED AT 250 WORDS)