Overexpression of Upf1p compensates for mitochondrial splicing deficiency independently of its role in mRNA surveillance

In yeast the UPF1, UPF2 and UPF3 genes encode three interacting factors involved in translation termination and nonsense-mediated mRNA decay (NMD). UPF1 plays a central role in both processes. In addition, UPF1 was originally isolated as a multicopy suppressor of mitochondrial splicing deficiency, and its deletion leads to an impairment in respiratory growth. Here, we provide evidence that inactivation of UPF2 or UPF3, like that of UPF1, leads to an impairment in respiratory competence, suggesting that their products, Upf1p, Upf2p and Upf3p, are equivalently involved in mitochondrial biogenesis. In addition, however, we show that only Upf1p acts as a multicopy suppressor of mitochondrial splicing deficiency, and its activity does not require either Upf2p or Upf3p. Mutations in the conserved cysteine- and histidine-rich regions and ATPase and helicase motifs of Upf1p separate the ability of Upf1p to complement the respiratory impairment of a Deltaupf1 strain from its ability to act as a multicopy suppressor of mitochondrial splicing deficiency, indicating that distinct pathways express these phenotypes. In addition, we show that, when overexpressed, Upf1p is not detected within mitochondria, suggesting that its role as multicopy suppressor of mitochondrial splicing deficiency is indirect. Furthermore, we provide evidence that cells overexpressing certain upf1 alleles accumulate a phosphorylated isoform of Upf1p. Altogether, these results indicate that overexpression of Upf1p compensates for mitochondrial splicing deficiency independently of its role in mRNA surveillance, which relies on Upf1p-Upf2p-Upf3p functional interplay.

MitBASE pilot: a database on nuclear genes involved in mitochondrial biogenesis and its regulation in Saccharomyces cerevisiae

In the framework of the EU BIOTECH PROGRAM and within the 'MITBASE: a comprehensive and integrated database on mtDNA' project, we have prepared a pilot database (MitBASE Pilot) on nuclear genes involved in mitochondrial biogenesis and its regulation in Saccharomyces cerevisiae. MitBASE Pilot includes nuclear genes encoding mitochondrial proteins as well as nuclear genes encoding products which are localised in other sub-cellular compartments but nevertheless interact with mitochondrial functions. Genes have been classified on the basis of the mitochondrial process in which they participate and the mitochondrial phenotype of the gene knockout. The structure of the MitBASE Pilot database has been conceived for a flexible organisation of the information. An intuitive visual query system has been developed which allows users to select information in different combinations, both in the query and the output format, according to their needs. MitBASE Pilot is a relational database, is maintained at the EMBL-European Bioinformatics Institute (EBI) and is available at the World Wide Web site http://www3.ebi.ac. uk/Research/Mitbase/mitbiog.pl

MitBASE: a comprehensive and integrated mitochondrial DNA database

MitBASE is an integrated and comprehensive database of mitochondrial DNA data which collects all available information from different organisms and from intraspecie variants and mutants. Research institutions from different countries are involved, each in charge of developing, collecting and annotating data for the organisms they are specialised in. The design of the actual structure of the database and its implementation in a user-friendly format are the care of the European Bioinformatics Institute. The database can be accessed on the Web at the following address: http://www.ebi.ac. uk/htbin/Mitbase/mitbase.pl. The impact of this project is intended for both basic and applied research. The study of mitochondrial genetic diseases and mitochondrial DNA intraspecie diversity are key topics in several biotechnological fields. The database has been funded within the EU Biotechnology programme.

The transcription of NAM7/UPF1 is enhanced in the absence of Cyp1p/Hap1p concomitant with the appearance of an ISF1-NAM7 cotranscript in Saccharomyces cerevisiae

The two adjacent nuclear genes ISF1 and NAM7 cooperatively participate in mitochondrial functions. It is well known that Cyp1p(Hap1p) activates a number of genes involved in these same functions. We show in this paper that Cyp1p influences the transcriptional regulation of NAM7. In addition, a significant amount of ISF1-NAM7 cotranscript is observed in a cyp1 mutant context. An extensive analysis of the intergenic region which separates the two genes revealed 5' starts of the NAM7 transcripts, additional to those previously mapped. These new 5' starts overlap the 3' ends of ISF1. We propose that NAM7 is under the control of a negative Cyp1p-dependent regulator and that its absence favours a transcriptional read-through which results in the ISF1-NAM7 cotranscript we have identified.

Post-epidemic serological survey for JE virus antibodies in south Arcot district (Tamil Nadu)

Following an extensive epidemic of Japanese encephalitis (JE) in 1981, a serological survey was carried out in the South Arcot district of Tamil Nadu in April 1982. Serum specimens were obtained from 10 villages with serologically proven infections and 6 villages with no reported case of encephalitis during the 1981 epidemic. The serum specimens tested for haemagglutination inhibition, complement fixing and neutralizing antibodies, showed a high prevalence of JE (49.17%), West Nile (40.78%) and dengue (18.14%) viruses with predominance of JE. The prevalence did not differ between the villages with or without Japanese encephalities. There was also no difference between the family members and neighbours.

Neutralizing antibody response to Japanese encephalitis inactivated mouse brain vaccine among laboratory personnel

Among vaccinees given two doses of JE Nakayama strain liquid vaccine, 41.8% had significant neutralizing (N) antibody response to the P20778 strain and 48.6% to the Japanese Nakayama strain. Among vaccinees who received three doses of the freeze-dried vaccine, the proportion of positive reactors was 53.8% when the sera were tested with the P20778 strain and 47.4% with the Nakayama strain. A fairly large proportion of those vaccinees who had responded positively to the latter vaccine were found to have lost detectable N antibodies to the P20778 strain and a smaller proportion to the Nakayama strain 13 to 17 months after the third dose of vaccine. Following the administration of a booster dose of the vaccine after this time interval, 65.2% and 56.5% of vaccinees responded positively to the P20778 strain and the Nakayama strain, respectively. The differences between the proportion of positive reactors to the two strains were not significant either for the liquid vaccine or the freeze-dried vaccine. An important finding was the priming effect of infection with West Nile (WN) virus before vaccination. Those vaccinees who had N antibody to WN virus before vaccination had a significantly higher N antibody response to the P20778 strain of JE virus than those who had no detectable antibody to WN virus. These findings indicate that the JE Nakayama strain vaccine would be efficacious in India, particularly in view of the widespread prevalence of WN virus infection.

Prevalence of antibodies to Japanese encephalitis and West Nile viruses among wild birds in the Krishna-Godavari Delta, Andhra Pradesh, India

In the Krishna-Godavari Delta region of the State of Andhra Pradesh, India, 866 sera obtained from trapped birds of 13 species were tested for neutralizing antibody to Japanese encephalitis (JE) virus; two species of birds belonging to the family Ardeidae, Ardeola grayii (pond heron) and Bubulcus ibis (cattle egret), contributed 514 of these sera. Neutralizing antibody to JE virus--i.e. sera giving positive reactions--was detected in 179 sera (34.8%) from these two species; in addition, two sera (0.4%) gave equivocal reactions, presumably indicating partial protection. There were only nine positive reactors (2.6%) among the remaining 352 sera from all other bird species. Of the 181 sera from ardeid birds in which neutralizing activity was detected, 174 were tested for neutralizing antibody to West Nile (WN) virus. The results indicated that 35.6% of these 179 sera had antibody specific to JE virus only and 63.8% possessed neutralizing antibodies to JE virus or to WN virus or to both; these figures represent 12.5% and 22.5% , respectively, of the total of 514 birds of these two species which were tested for neutralizing antibody to JE virus. The findings suggest that ardeid birds may be involved in the natural cycle of JE virus and, possibly, also of WN virus in India.