TAP, the human homolog of Mex67p, mediates CTE-dependent RNA export from the nucleus

The constitutive transport element (CTE) of the type D retroviruses promotes nuclear export of unspliced viral RNAs apparently by recruiting host factor(s) required for export of cellular messenger RNAs. Here, we report the identification of TAP as the cellular factor that specifically binds to wild-type CTE but not to export-deficient CTE mutants. Microinjection experiments performed in Xenopus oocytes demonstrate that TAP directly stimulates CTE-dependent export. Furthermore, TAP overcomes the mRNA export block caused by the presence of saturating amounts of CTE RNA. Thus, TAP, like its yeast homolog Mex67p, is a bona fide mRNA nuclear export mediator. TAP is the second cellular RNA binding protein shown to be directly involved in the export of its target RNA.

Studies on the heterologous expression of BstVI restriction endonuclease in Escherichia coli

Bacterial restriction and modification systems must be regulated to avoid self-restriction. It is generally accepted that cognate DNA methyltransferases normally protects both, the host's chromosome and extrachromosomal elements from the activity of their endonuclease counterparts. When the bstVIRM genes from Bacillus stearothermophilus V were subcloned into Escherichia coli, several clones exhibiting a r+m- phenotype were originated. The present work was undertaken to analyze the possibility that mechanisms other than DNA methylation could account for the viability of these cells. No evidence was found for an inhibitory agent or endonuclease compartmentation. In vivo experiments showed that lambda phage multiplication was poorly restricted by the heterologous enzyme. The restricting activity against the incoming phase increased however when phage adsortion was performed at higher temperatures. Analogous experiments in which a DNA-repair deficient strain was used as a host for the thermophilic R-M system suggested, to some extent, the participation of the repair machinery in the viability of r+m- clones.

Anti-EBNA-1 (carboxy-half) IgG antibodies as a seroepidemiological marker for Epstein-Barr virus infection

A population of 2,024 voluntary blood donors was tested for anti-EBNA-1 IgG and anti-VCA IgG serum antibodies to define the EBV infection rate and to compare two different epidemiological markers. Initial screening was performed with a sensitive EBNA-1-IgG ELISA based on recombinant antigen (Biotest) and a VCA-IgG ELISA based on conventional antigen. Both ELISAs had concordant results in 90.4% of the sera. The infection rate was found to be 96.8%. The expected immune status VCA+/EBNA+ was observed in 98.1% of the seropositives. The comparison of sensitivity, specificity, and predictive values between the two screening assays underlines the superiority of the EBNA-1 ELISA. The marker anti-EBNA-1 IgG as detected by a sensitive ELISA (Biotest anti-EBV recombinant) is suitable for defining previous EBV infection (positive predictive value 99.8%). The high infection rate in the adult population, however, renders the supply with EBV-negative blood rather difficult.

Quantitative trait loci analysis affecting contextual conditioning in mice

In an extensive backcross of mice between C3H/HeJ (C3H) and C57BL/6J (B6), we sought to map genes that influence learning and memory as measured by performance in a contextual fear-conditioning paradigm. Our results indicate that there are several genetic regions that have a strong influence on performance in this paradigm. The strongest influences map to the proximal and distal ends of chromosome 1 (lod scores of 5.14 and 4.76, respectively). Other chromosomal regions (chromosomes 3, 7, 8, 9 and 18) were also identified as candidates for regions containing genes influencing contextual fear conditioning, with lod scores ranging from 1.8 to 2.7.

Phylogenetic evidence for role-reversals of gender-associated mitochondrial DNA in Mytilus (Bivalvia: Mytilidae)

Distinct gender-associated mitochondrial DNA (mtDNA) lineages (i.e., lineages which are transmitted either through males or through females) have been demonstrated in two families of bivalves, the Mytilidae (marine mussels) and the Unionidae (freshwater mussels), which have been separated for more than 400 Myr. The mode of transmission of these M (for male-transmitted) and F (for female-transmitted) molecules has been referred to as doubly uniparental inheritance (DUI), in contrast to standard maternal inheritance (SMI), which is the norm in animals. A previous study suggested that at least three origins of DUI are required to explain the phylogenetic pattern of M and F lineages in freshwater and marine mussels. Here we present phylogenetic evidence based on partial sequences of the cytochrome c oxidase subunit I gene and the 16S RNA gene that indicates the DUI is a dynamic phenomenon. Specifically, we demonstrate that F lineages in three species of Mytilus mussels, M. edulis, M. trossulus, and M. californianus, have spawned separate lineages which are now associated only with males. This process is referred to as "masculinization" of F mtDNA. By extension, we propose that DUI may be a primitive bivalve character and that periodic masculinization events combined with extinction of previously existing M types effectively reset the time of divergence between conspecific gender-associated mtDNA lineages.

The simian retrovirus-1 constitutive transport element, unlike the HIV-1 RRE, uses factors required for cellular mRNA export

BACKGROUND

A hallmark of retroviral gene expression is that unspliced retroviral genomic RNA is exported to the cytoplasm, whereas endogenous intron-containing cellular RNAs are usually retained in the nucleus. In complex retroviruses, such as human immunodeficiency virus-1 (HIV-1), nuclear export is accomplished by the interaction of a virally encoded protein, Rev, with a cis-acting RNA element, the Rev-responsive element (RRE). In type D retroviruses, such as the simian retrovirus type 1 (SRV-1), however, genomic RNA is exported by cellular factor(s) that interact with a conserved cis-acting RNA element, the constitutive transport element (CTE).

RESULTS

We found that the CTE was exported in a specific and saturable fashion from Xenopus oocyte nuclei. When inserted into the intron of an adenovirus-derived pre-mRNA, the CTE did not affect splicing efficiency but promoted the nuclear export of the excised intron lariat that is normally retained within the nucleus. Export of CTE-containing RNAs to the cytoplasm was not affected by the heterogeneous nuclear ribonucleoprotein A1 or an excess of peptides corresponding to the Rev nuclear export signal. Microinjection of saturating amounts of CTE RNA did not affect tRNA export or Rev-mediated export but did inhibit mRNA export. CTE-mediated export was found to be dependent on Ran-mediated GTP hydrolysis.

CONCLUSION

The Rev-RRE system and the CTE direct intron-containing RNAs to distinct export pathways. Although previous data have suggested that Rev uses the same export pathway as uracil-rich small nuclear RNAs and 5S ribosomal RNA, the CTE seems to interact with evolutionarily conserved factors that are essential for cellular mRNA export.

Male-dependent doubly uniparental inheritance of mitochondrial DNA and female-dependent sex-ratio in the mussel Mytilus galloprovincialis

We have investigated sex ratio and mitochondrial DNA inheritance in pair-matings involving five female and five male individuals of the Mediterranean mussel Mytilus galloprovincialis. The percentage of male progeny varied widely among families and was found to be a characteristic of the female parent and independent of the male to which it was mated. Thus sex-ratio in Mytilus appears to be independent of the nuclear genotype of the sperm. With a few exceptions, doubly uniparental inheritance (DUI) of mtDNA was observed in all families fathered by four of the five males: female and male progeny contained the mother's mtDNA (the F genome), but males contained also the father's paternal mtDNA (the M genome). Two hermaphrodite individuals found among the progeny of these crosses contained the F mitochondrial genome in the female gonad and both the F and M genomes in the male gonad. All four families fathered by the fifth male showed the standard maternal inheritance (SMI) of animal mtDNA: both female and male progeny contained only the maternal mtDNA. These observations illustrate the intimate linkage between sex and mtDNA inheritance in species with DUI and suggest different major roles for each gender. We propose a model according to which development of a male gonad requires the presence in the early germ cells of an agent associated with sperm-derived mitochondria, these mitochondria are endowed with a paternally encoded replicative advantage through which they overcome their original minority in the fertilized egg and this advantage (and, therefore, the chance of an early entrance into the germ line) is countered by a maternally encoded egg factor.

Regulation of mRNA export in response to stress in Saccharomyces cerevisiae

The response of eukaryotic cells to heat shock and other forms of stress occurs at both transcriptional and post-transcriptional levels. We used in situ hybridization to determine whether stress affected the subcellular distribution of poly(A)+ RNA in Saccharomyces cerevisiae. Following induction of stress by either heat shock (42 degrees C) or addition of a high concentration of ethanol (10%), the nucleocytoplasmic export of most poly(A)+ RNA was blocked. In situ hybridization indicated that heat-inducible SSA4 and SSA1 mRNAs were exported from nuclei under these same conditions. On the other hand, both GAL1 and URA3 transcripts expressed from the SSA4 promoter accumulated in nuclei following heat shock. Sequences within either the 5' 1600 or the 3' 500 nucleotides of SSA4 mRNA were sufficient to direct GAL1 mRNA to the cytoplasm during stress. The export of SSA4 mRNA following stress required functional nuclear pore complexes, as SSA4 mRNA accumulated in nuclei following heat shock of cells containing temperature-sensitive nucleoporins. However, the selective export of SSA4 mRNA was maintained in heat-shocked cells carrying temperature-sensitive alleles of RNA1, PRP20, or an inducible dominant-negative allele of GSP1, the S. cerevisiae homolog of RAN/TC4. The results reported here suggest that there is selective export of mRNA in yeast.

Species-specific segregation of gender-associated mitochondrial DNA types in an area where two mussel species (Mytilus edulis and M. trossulus) hybridize

In each of the mussel species Mytilus edulis and M. trossulus there exist two types of mtDNA, the F type transmitted through females and the M type transmitted through males. Because the two species produce fertile hybrids in nature, F and M types of one may introgress into the other. We present the results from a survey of a population in which extensive hybridization occurs between these two species. Among specimens classified as "pure" M. edulis or "pure" M. trossulus on the basis of allozyme analysis, we observed no animal that carried the F or the M mitotype of the other species. In most animals of mixed nuclear background, an individual's mtDNA came from the species that contributed the majority of the individual's nuclear genes. Most importantly, the two mtDNA types in post-F1 male hybrids were of the same species origin. We interpret this to mean that there are intrinsic barriers to the exchange of mtDNA between these two species. Because such barriers were not noted in other hybridizing species pairs (many being even less interfertile than M. edulis and M. trossulus), their presence in Mytilus could be another feature of the unusual mtDNA system in this genus.

Male and female mitochondrial DNA lineages in the blue mussel (Mytilus edulis) species group

In blue mussels of the Mytilus edulis species complex, mitochondrial DNA (mtDNA) inheritance is coupled with gender. Females receive their mother's mtDNA and pass it on to both their daughters and sons. In addition, males receive mtDNA from their father and transmit this male mtDNA to their sons. If this pattern of "doubly uniparental inheritance" is older than the M. edulis species complex, then all members of this group must have two distinct mtDNA lineages: a maternal lineage that is transmitted through females and a paternal lineage that is transmitted through males. To test this hypothesis, we scored mtDNA variation in two taxa in this complex, M. edulis and M. trossulus, by means of restriction fragment profiles of whole-mtDNA genomes and DNA sequence of a region of the cytochrome c oxidase subunit III gene (COIII). The various mitotypes present in these mussels were classified as "male" or "female" based on their gender association and as belonging to M. edulis or M. trossulus based on species-specific allozymes. Both maximum parsimony and neighbor-joining phylogenies based on the COIII sequences grouped female and male mtDNAs into two distinct lineages irrespective of specific origin in accordance with the hypothesis that the origin of these lineages predates the divergence of M. edulis and M. trossulus.

The GTP-bound form of the yeast Ran/TC4 homologue blocks nuclear protein import and appearance of poly(A)+ RNA in the cytoplasm

Ran/TC4, a Ras-like GTP-binding protein, and its nucleotide exchanger, RCC1, have been implicated in control of protein movement into the nucleus and cytoplasmic accumulation of mRNA. Saccharomyces cerevisiae contains two homologues of the mammalian Ran/TC4, encoded by the GSP1 and GSP2 genes. We have constructed yeast strains that overproduce either wild-type Gsp1 or a form of Gsp1 with glycine-21 converted to valine (Gsp1-G21V), which we show stabilizes the GTP-bound form. Cells producing Gsp1-G21V have defects in localization of nuclear proteins; nuclear proteins accumulate in the cytoplasm following galactose induction of Gsp1-G21V. Similarly, cells producing Gsp1-G21V retain poly(A)+ RNA in their nuclei. These findings suggest that hydrolysis of GTP by Ran/TC4 is necessary for proper import of proteins into the nucleus and appearance of poly(A)+ RNA in the cytoplasm.

An unusual type of mitochondrial DNA inheritance in the blue mussel Mytilus

In animals, mitochondrial DNA (mtDNA) inheritance is predominantly maternal. In a few cases incidental transmission of paternal mtDNA was observed and estimated to account for only 10(-4)-10(-3) of an individual's mtDNA content. In contrast, biparental inheritance is common in mussels of the genus Mytilus. Here we present direct evidence that sex and mtDNA inheritance are coupled in Mytilus. Females inherit mtDNA only from their mother, but they transmit it to both daughters and sons. Males inherit mtDNA from both parents, but they transmit to sons only the mtDNA they inherited from their father. In pair matings, this mtDNA inheritance pattern is associated with a strong sex-ratio bias. These findings establish a newly discovered type of cytoplasmic DNA transmission. We also present evidence that the phenomenon breaks down in interspecific hybrids.

The expression of the bstVIM gene from Bacillus stearothermophilus V is restricted to vegetative cell growth

The activity of BstVI DNA methyltransferase was monitored during the sporulative cycle of Bacillus stearothermophilus V. Significant methylase activity was found only in bacteria growing vegetatively. This was confirmed by Northern hybridization, which indicated that the bstVIM gene was not transcribed in cells undergoing sporulation. Supporting evidence came from experiments which demonstrated that the RNA polymerase holoenzyme from these cells did not recognize the promoter elements upstream of the bstVIM gene.

Maximal anaerobic performance of the knee extensor muscles during growth

The extent of the growth changes in maximal work output during 10 s (MWO10), 30 s (MWO30), and 90 s (MWO90) of maximal repetitive knee flexions and extensions assessed on a modified Hydra-Gym machine was investigated in 84 boys and 83 girls, 9-19 yr of age. Body weight, fat mass and fat free mass by underwater weighing, and thigh volume and cross-sectional area were also determined. No difference was observed in the absolute MWO10, MWO30, and MWO90 between girls and boys at 9 and 11 yr of age. However, significant differences appeared between genders from 13 yr of age onward, anaerobic performances of the knee extensor muscles of girls representing about 75% or even less of those of boys. The analysis of variance revealed that maximal work ouput during the three knee extension tests was significantly greater in males as well as in females from 9 to 18 yr, regardless how performance was related to morphological characteristics. Performance in absolute values or expressed per unit of body weight, fat free mass, and thigh cross-sectional area for the MWO10, MWO30, and MWO90 tests were almost always significantly lower in both genders when performances of the 9-yr-old group were compared with those of the 13-yr-old group or older groups. Improvement in maximal work output during the 10-s, 30-s, or 90-s knee extension tests with age occurred mainly between 9 and 15 yr in both genders. The results of the present study show that there are gender differences in predominantly anaerobic performances during growth and reveal that increase in muscle mass does not appear to be the only factor responsible for the age-related increment in the anaerobic working capacity of the knee extensor muscles.

Cloning the BstVI restriction-modification system in Escherichia coli

A standard DNA modification methyltransferase (MTase) selection protocol was followed to clone the BstVI restriction and modification system from Bacillus stearothermophilus in Escherichia coli. Both genes were contained in a 4.4-kb EcoRI fragment from B. stearothermophilus V chromosomal DNA. The heterologous expression of these genes did not depend on their orientation in the vector, suggesting that the genes are expressed in E. coli under the control of promoters located on the cloned fragment. Subcloning experiments demonstrated that the bstVIR gene was expressed in the absence of its cognate MTase.