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W R Hess

Publications and source records attributed to W R Hess.

At least 37 records · Page 2Linked to original sources
PubMed1997

Precise branch point mapping and quantification of splicing intermediates.

Lariat intermediates of a group II intron were investigated via RT-PCR. Several reverse transcriptases appeared capable of reading through a branched nucleotide. A new method has been established that yields precise information about the location of the branch point within an intron. As an extension of our approach, antisense transcripts of the previously cloned PCR products were successfully used in RNase Protection Assays, providing a tool for quantification of splicing intermediates. Application of the method presented to other self-splicing introns as well as introns in nuclear pre-mRNAs is envisaged.

Base Sequence↗
PubMed1997

Localization of an open reading frame with homology to human aspartoacylase upstream from psbA in the prokaryote Prochlorococcus marinus CCMP 1375.

An open reading frame encoding a polypeptide with significant homology (about 28% identity and 16% similarity) to human aspartoacylase (ASPA) was identified in the genome of Prochlorococcus marinus CCMP 1375, an oxyphototrophic bacterium. Sequence alignments show that, in particular, the regions previously suggested to form the catalytic core of human ASPA are evolutionarily conserved and nearly identical to that found in the Prochlorococcus putative ASPA. A glutamate at position 273 is located central to the strongly conserved INEAAY motif and corresponds to a glutamate-285 in human ASPA. A point mutation at this site, resulting in a Glu285Ala missense mutation, was identified previously as the molecular basis for Canavan disease, a form of leukodystrophy. The data provide new insights about conserved and hence functionally important domains of ASPA. The detection of this gene in an unicellular prokaryote demonstrates that this enzymatic activity is more widespread than expected previously. Furthermore, bacteria may be used as simple model organisms to study different forms of ASPA.

Amidohydrolases↗
PubMed1996

Coexistence of phycoerythrin and a chlorophyll a/b antenna in a marine prokaryote.

Prochlorococcus marinus CCMP 1375, a ubiquitous and ecologically important marine prochlorophyte, was bound to possess functional genes coding for the alpha and beta subunits of a phycobiliprotein. The latter is similar to phycoerythrins (PE) from marine Synechococcus cyanobacteria and bind a phycourobilin-like pigment as the major chromophore. However, differences in the sequences of the alpha and beta chains compared with known PE subunits and the presence of a single bilin attachment site on the alpha subunit designate it as a novel PE type, which we propose naming PE-III. P. marinus is the sole prokaryotic organisms known so far that contains chlorophylls a and b as well as phycobilins. These data strongly suggest that the common ancestor of prochlorophytes and the Synechococcus cyanobacteria contained phycobilins. Flow cytometric data from the tropical Pacific Ocean provide evidence that deep populations of Prochlorococcus possess low amounts of a PE-like pigment, which could serve either in light harvesting or nitrogen storage or both.

Amino Acid Sequence↗
PubMed1996

Impaired splicing of the rps12 transcript in ribosome-deficient plastids.

Analysis of RNA maturation in ribosome-deficient plastids of four non-allelic barley mutants revealed an increased accumulation and altered processing of transcripts of the ribosomal protein gene CS12 (rps12) compared to normal chloroplasts. The three exons of rps12 are part of two different polycistronic transcription units. Generation of mature rps12-mRNA involves both cis- and trans-splicing. In ribosome-deficient plastids, the cis-intron separating exons 2 and 3 remains entirely unspliced whereas the splicing of the bipartite rps12 trans-intron between exon 1 and exon 2 occurs, but at a reduced level. A comparison of the 3' and 5' ends of the two RNAs that are generally assumed to interact during trans-splicing showed a difference in the processing pathways of 3' rps12 transcripts between mutated and normal chloroplasts. Nonetheless, the final products were identical.

Base Sequence↗
PubMed1995

Characterization of the single psbA gene of Prochlorococcus marinus CCMP 1375 (Prochlorophyta).

DNA sequence, copy number, expression and phylogenetic relevance of the psbA gene from the abundant marine prokaryote P. marinus CCMP 1375 was analyzed. The 7 amino acids near the C-terminus missing in higher plant and in Prochlorothrix hollandica D1 proteins are present in the derived amino acid sequence. P. marinus contains only a single psbA gene. Thus, this organism lacks the ability to adapt its photosystem II by replacement of one type of D1 by another, as several cyanobacteria do. Phylogenetic trees suggested the D1-1 iso-form from Synechococcus PCC 7942 as the next related D1 protein and place P. marinus separately from Prochlorothrix hollandica among the cyanobacteria.

Amino Acid Sequence↗
PubMed1995

Sequencing of RAPD fragments amplified from the genome of the prokaryote Prochlorococcus marinus (prochlorophyta).

DNA fingerprint patterns from the chlorophyll a and b containing prokaryote Prochlorococcus marinus were generated with the RAPD technique using two primers derived from repetitive sequence motifs, [(GATA)4 and M13] and a random primer (OPB-10]. Five RAPD fragments were reamplified, cloned and sequenced. The clones M13/1300 and OPB-10/1100 contained open reading frames, whereas the (GATA)4 fragments were interrupted by stop codons in all frames indicating their noncoding function and possessed a high AT score of 63% and 71%, respectively. With the two (GATA)4 clones and the M13/300 clone strain-specific signals were obtained in a Southern blot analysis of various Prochlorococcus strains. Clones M13/1300 and OPB-10/1100, containing the ORFs, produced RFLPs between the strains analyzed. All RAPD fragments are represented as single copy in the genome of Prochlorococcus.

Bacteria↗
PubMed1994

Ribosome-deficient plastids affect transcription of light-induced nuclear genes: genetic evidence for a plastid-derived signal.

Transcription of ten nuclear genes was analysed in the albostrians mutant of barley (Hordeum vulgare L.). The lack of plastid ribosomes in white seedlings of this mutant results in a complex alteration of nuclear gene expression at the transcriptional level. We found a strong reduction in the accumulation of mRNAs transcribed from nuclear genes encoding chloroplast enzymes involved in the Calvin cycle, the chlorophyll a/b binding protein, and the cytosolic enzyme nitrate reductase. In contrast, the levels of transcripts of the genes encoding the cytosolic glycolytic enzymes glyceraldehyde phosphate dehydrogenase and phosphoglycerate kinase were slightly enhanced. Accumulation of chalcone synthase mRNA even reaches much higher levels in white than in green leaves. Ribosome-deficient plastids were combined by crossing with a nuclear genotype heterozygous for the albostrians allele. Analysis of transcript levels in F1 plants having the same nuclear genotype and differing only with respect to their content of normally developed chloroplasts versus undifferentiated mutant plastids, provided strong genetic evidence for the plastid being the origin of a signal (chain) involved in regulation of nuclear gene expression. Results of run-on transcription in isolated nuclei demonstrated that the plastid signal acts at the level of transcription; it does not interfere with gene regulation in general. Mechanisms triggering nuclear gene expression in response to light operate in white mutant leaves: the very low levels of mRNAs derived from nuclear genes encoding chloroplast proteins and the strongly enhanced level of chalcone synthase mRNA were both light inducible. Also the negative regulation of leaf thionein gene expression by light is observed in white albostrians seedlings.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell Nucleus↗
PubMed1994

Attempted transovarial and venereal transmission of African swine fever virus by the Iberian soft tick Ornithodoros (Pavlovskyella) marocanus (Acari: Ixodoidea: Argasidae).

Transovarial transmission experiments were conducted with three groups of Ornithodoros (Pavlovskyella) marocanus Velu; one group consisted of 27 pairs of adults that had been fed as larvae on a pig with a viremia of 10(7.4) HAd50/ml of African swine fever virus (ASFV). The second and third groups each consisted of 100 pairs of adults fed on a viremic pig (10(4.5) HAd50/ml) as adults. The first group underwent five gonotrophic cycles over a 554-d period. The second and third groups underwent three and two gonotrophic cycles, respectively. All larvae were fed in individual cohorts on naive pigs and the resulting nymphs were assayed by cohort for ASFV. None of the larvae transmitted ASFV to naive pigs by bite and ASFV was not isolated in swine buffy coat cultures from any cohort of nymphs. Therefore, O. marocanus does not exhibit transovarial transmission of ASFV. Venereal transmission experiments were conducted with pairs of O. marocanus in which either the female (100 pairs) or the male (100 pairs), respectively, had fed on a viremic pig (10(4.5) HAd50/ml). Both groups underwent at least two gonotrophic cycles over a 470-d period, were sampled periodically for the presence of ASFV, and the progeny were tested for the presence of ASFV. Venereal transmission from male to female occurred in 10% (1/10) of O. marocanus after the first gonotrophic cycle, but not after the second or third gonotrophic cycle, and transovarian transmission in these groups was not observed. Venereal transmission from infected females to uninfected males did not occur. ASFV persisted through five gonotrophic cycles over a 554-d period in 30% of adults fed on a viremic pig as larvae. ASFV was cleared during three gonotrophic cycles within a year from nearly all ticks fed on a viremic pig as adults. Virus-induced mortality rats of 12-80% occurred among ticks fed on viremic animals, whereas, no mortality was seen in ticks fed on uninfected animals. ASFV infection in ticks did not effect feeding frequency, egg-hatch rate, or the oviposition rate among females fed on a viremic pig as adults. The oviposition rate for females fed on a viremic pig as larvae was reduced by 63.4%. Parthenogenesis was not observed among O. marocanus. The mean gonotrophic cycle duration for pig-fed O. marocanus at 27 degree C was 19.8 d and the mean fecundity was 88.3 +/- 17.9 eggs/female/gonotrophic cycle.

African Swine Fever↗
PubMed1994

Inefficient rpl2 splicing in barley mutants with ribosome-deficient plastids.

Analysis of transcript accumulation and splicing in plastids of four nuclear mutants of barley revealed that the ribosomal protein L2 (rpl2) gene transcripts containing a group II intron remained entirely unspliced, whereas the intron of the ribosomal protein L16 (rpl16) gene (linked with the rpl2 gene in the same operon) was removed in the mutant plastids. Also, the transcripts of other genes containing group II introns (ribosomal protein S16 gene, rps16; NADH dehydrogenase ND2 gene, ndhB; cytochrome f gene, petD; and intron-containing reading frame 170, irf170) and of the tRNA for leucine, trnL (UAA), possessing the only chloroplast group I intron, were found to be spliced. The mutants used in this investigation are considered to be nonallelic; this excludes the possibility that a single nuclear gene is responsible for the impaired splicing of rpl2 transcripts. The mutants, however, have a severe deficiency in chloroplast ribosomes in common; this deficiency is evident from the lack of the essential ribosomal protein L2 and from an extremely low steady state level of plastid rRNAs. From these results, we conclude that a functioning translational apparatus of the organelle is a prerequisite for splicing of the chloroplast rpl2 class II intron but not for splicing of at least five other group II intron-containing transcripts. This provides genetic evidence for a chloroplast DNA-encoded component (e.g., a maturase) involved in the splicing of rpl2 pre-mRNA.

Base Sequence↗
PubMed1993

Chloroplast rps15 and the rpoB/C1/C2 gene cluster are strongly transcribed in ribosome-deficient plastids: evidence for a functioning non-chloroplast-encoded RNA polymerase.

Transcription of plastid genes and transcript accumulation were investigated in white leaves of the albostrians mutant of barley (Hordeum vulgare) and in heat-bleached leaves of rye (Secale cereale) as well as in normal green leaves of both species. Cells of white leaves of the mutant and cells of heat-bleached leaves bear undifferentiated plastids lacking ribosomes and, consequently, plastid translation products, among them the subunits of a putative chloroplast RNA polymerase encoded by the plastid genes rpoA, B, C1 and C2. The following results were obtained. (i) Plastid genes are transcribed despite the lack of chloroplast gene-encoded RNA polymerase subunits. The plastid origin of these transcripts was proven. This finding provides evidence for the existence of a plastid RNA polymerase encoded entirely by nuclear genes. (ii) Transcripts of the rpo genes and of rps15, but not of genes involved in photosynthesis and related processes (psbA, rbcL, atpI-H), were abundantly accumulated in ribosome-deficient plastids. In contrast, chloroplasts accumulated transcripts of photosynthetic, but not of the rpo genes. (iii) Differences in transcript accumulation between chloroplasts and ribosome-deficient plastids are due to different relative transcription rates and different transcript stability. (iv) The observed differences in transcription are not caused by an altered pattern of methylation of plastid DNA. Thus, the prokaryotic plastid genome of higher plants is transcribed by two RNA polymerases. The observed differences in transcription between chloroplasts and undifferentiated plastids might reflect different functions of the two enzymes.

Chloroplasts↗
PubMed1993

Editing of the chloroplast rpoB transcript is independent of chloroplast translation and shows different patterns in barley and maize.

Sequence analysis of amplified cDNAs derived from the maize chloroplast rpoB transcript which encodes the beta subunit of a chloroplast specific, DNA dependent RNA polymerase reveals four C-to-U editing sites clustered within 150 nucleotides of the 5' terminal region of the rpoB message. These newly identified editing sites confirm the bias of chloroplast editing for certain codon transitions and for second codon positions which both appear suggestive for an involvement of the translational apparatus in the editing process. This supposition prompted us to investigate editing of the rpoB transcript from ribosome deficient, and hence protein synthesis deficient, plastids of the barley mutant albostrians. In this mutant editing is, however, not impaired at any of the editing sites functional in the barley wild type rpoB transcript. This demonstrates that chloroplast editing is neither linked to nor dependent on the chloroplast translational apparatus. As a further consequence any peptide components required for chloroplast editing must be encoded in the nuclear genome. In spite of strong sequence conservation only three of the four editing sites identified in the maize rpoB transcript are functional in barley. This indicates that sequences surrounding an editing site alone are not sufficient as determinants for the editing process in chloroplasts, but that trans-acting templates carrying the editing information for each individual site may also be required.

Amino Acid Sequence↗
PubMed1992

Experimental transmission of African swine fever virus by the soft tick Ornithodoros (Pavlovskyella) marocanus (Acari: Ixodoidea: Argasidae).

A total of 1,600 Ornithodoros (Pavlovskyella) marcocanus larvae were fed on a pig with a viremia of 10(7.4) HAd50/ml of African swine fever virus (ASFV). Infected larvae were sampled daily for 15 d, and nymphs were sampled at least once per instar until they became adults. Initial titers of 10(4.48) HAd50 per larva declined to 10(4.04) within 2 d. Larval titers reached a maximum of 10(6.0) HAd50 per larva 10 d after the infective blood meal. Nymphs of each instar were fed on a susceptible pig and in each case transmitted ASFV by bite. Virus titers for first to fourth instars ranged from 10(4.61) to 10(3.34) HAd50 per nymph. Transstadial survival occurred in subsequent first, second, third, and fourth instars with an 89% survival rate over 250 d. Approximately 30% of adult ticks that were infected as larvae remained infected and transmitted ASFV to susceptible pigs 588 d later. In addition, ASFV was recovered from the same adult ticks 655 d after the infective blood meal.

African Swine Fever↗
PubMed1992

African swine fever virus infection in the Iberian soft tick, Ornithodoros (Pavlovskyella) marocanus (Acari: Argasidae).

One thousand six hundred Ornithodoros (Pavlovskyella) marocanus Velu larvae were fed on a pig infected with African swine fever virus (titer: 10(7.4) HAd50/ml), and 1,600 larvae were fed on an uninfected pig. Ticks in each group were compared for mortality rates, mean time to death for ticks that died, mean time from feeding to either molting or eclosion, percentage of ticks that eclosed or molted, and the number of blood meals per nymph or instar. Cumulative virus-induced mortality for all immature stages (larvae to adult) of O. marocanus that had been fed as larvae on a pig infected with African swine fever was ca. 73% over a 390-d period. In contrast, less than 9% mortality was observed among ticks fed on uninfected pigs. Mean time to death for infected ticks was 15-87 d versus 10-17 d for uninfected ticks. Differences in the premolt period (number of days from blood meal to molt) between infected and control ticks were not observed. Mean premolt periods for larvae and first-, second-, third-, fourth-, and fifth-instar nymphs fed on pigs were 7, 9, 15, 11, 15, and 15 d, respectively. The majority of infected and all uninfected ticks required only one blood meal from pigs to molt. Mean weights for unfed second-, third-, and fourth-instar nymphs and males and females were 0.50, 0.67, 3.07, 3.63, and 5.91 mg, respectively.

African Swine Fever↗
PubMed1992

African swine fever virus infection in the soft tick, Ornithodoros (Alectorobius) puertoricensis (Acari: Argasidae).

In total, 1,186 second instar Ornithodoros (Alectorobius) puertoricensis Fox second instars were fed on a pig when it had a viremia of 10(5.2) hemadsorption units (HAd50/ml) and 420 second-instar O. puertoricensis were fed on an uninfected pig. Subsequent blood meals for ticks in both groups were from uninfected pigs. The effects of African swine fever virus (ASFV) infection on O. puertoricensis populations were evaluated for the following parameters: mortality; mean time to death; percentage molted per instar; percentage molted to male, female, or subsequent instar; effects on duration of premolt period; and the number of blood meals per instar. The cumulative virus-induced mortality rate for all immature stages (second to fifth instar) of O. puertoricensis that had been fed as second instars on a pig infected with ASFV was 43.2%. In contrast, 23.1% mortality was observed among ticks fed on uninfected pigs. The mortality rate among third instars that fed on the viremic pig was 55.3% versus 4.8% among nymphs fed on normal pigs. One-third to more than one-half of all third, fourth, and fifth instars required at least two blood meals to molt. Mean premolt periods for second, third, fourth, fifth, and sixth instars fed on uninfected pigs were approximately 12, 15, 32, 22, and 14 d, respectively. Mean weights for unfed second to fifth instars, males, and females were: 0.6, 1.0, 1.5, 1.7, 1.5, and 3.1 mg per tick, respectively.

African Swine Fever↗
PubMed1991

Experimental transmission of African swine fever virus by the tick Ornithodoros (Alectorobius) puertoricensis (Acari: Argasidae).

The soft tick Ornithodoros puertoricensis Fox has been found on the Caribbean island of Hispaniola (Haiti and the Dominican Republic) where African swine fever (ASF) was endemic from 1978 to 1984. To evaluate the vector potential of O. puertoricensis for African swine fever virus (ASFV), second-instar nymphs were experimentally infected by feeding on a viremic pig that was infected with the Dominican Republic isolate (DR-II) of ASFV. Subsequent infection rates and mean virus titers for individually triturated ticks were: second-instar nymph (95.4%, 10(4.38 +/- 0.85)), third-instar nymph (48.9%, 10(4.59 +/- 0.61)), male (46.7%, 10(4.36 +/- 0.61)), and female (35.3%, 10(4.38 +/- 1.09)). Infected ticks transmitted ASFV to susceptible pigs by bite 23, 85, 126, 160, 182, and 239 d after the infective blood meal. These findings show that ASFV is passed transstadially among O. puertoricensis and that O. puertoricensis can be an efficient vector of African swine fever virus.

African Swine Fever↗
PubMed1989

A mouse lethal dose assay for detection and titration of Cowdria ruminantium (Kwanyanga strain) in goats and ticks.

A mouse lethal dose assay was used to detect a mouse pathogenic strain (Kwanyanga) of Cowdria ruminantium, the etiological agent of heartwater in goats and ticks. The titer of the rickettsial organisms in goat blood was directly related to the febrile response of the goat and the rickettsia were undetectable after the fever subsided. The maximum rickettsial titer in goat blood was 10(3) mouse LD50 ml-1. Cowdria-infected goat blood was shown to retain infectivity when held on ice for up to 2 h, but when held at room temperature infectivity declined by greater than 50% in 2 h. The mouse assay detected Cowdria in feeding female Amblyomma variegatum only on the eighth day of feeding and in feeding males on the second and eleventh days of feeding. Cowdria was shown to persist in the hemolymph of the soft tick Ornithodoros coriaceus for a period of at least 2 years.

Animals↗
PubMed1989

Clearance of African swine fever virus from infected tick (Acari) colonies.

Three laboratory colonies of the argasid tick Onithodoros moubata porcinus van der Merwe were started from collections made in 1983 at three different sites in Zimbabwe. All of the colonies contained ticks infected with African swine fever (ASF) virus that was readily transmitted by bite to domestic pigs. Although they were maintained on virus-free pig blood, ASF virus infections persisted in the colonies for at least 1 yr. Despite the fact that ASF virus passes transstadially, sexually, and transovarially in this tick species sometime during the following year, the virus disappeared from the colonies. Studies comparing fecundity in infected and uninfected lots of O. moubata porcinus showed that mortality rates were considerably higher among the infected ticks. A similar study with Ornithodoros erraticus Lucas, a tick that harbors and transmits ASF virus on the Iberian Peninsula, gave essentially the same results. This is probably a factor involved in the clearance of ASF virus from tick populations that are not subjected to reinfection. How this information may be applied in the eradication of African swine fever in Portugal and Spain is discussed.

African Swine Fever↗