As a consequence of the presence of both mitochondria and chloroplasts in plant cells there is a higher sorting requirement in a plant cell than that in a non-plant cell. Reflecting this, protein import to mitochondria and chloroplasts has been shown to be highly specific. However, there is a group of proteins which are encoded by a single gene in the nucleus, translated in the cytosol and targeted to both mitochondria and chloroplasts. These proteins are referred to as dual targeted proteins. The first protein shown to be dual targeted was pea glutathione reductase (GR). The focus of this thesis is the targeting properties of the dual targeted protein glutathione reductase. In order to overcome the limitations with traditional in vitro import systems we have developed an import system for simultaneous import of precursor proteins into mitochondria and chloroplasts (dual import system). The chloroplastic precursor of the small subunit of ribulose bisphosphate carboxylase/oxygenase (SSU) was mis-targeted to pea mitochondria in a single import system, but was imported only into chloroplasts in the dual system. The dual GR reductase precursor was targeted to both mitochondria and chloroplasts in both the single and dual import system. We have investigated the targeting and processing properties of the GR targeting signal. Using N-terminal truncations we have demonstrated that the GR targeting signal has a domain organisation. Our results show that GR has evolved a dual targeting signal with the C-terminal part being sufficient for chloroplast import, the internal part required for the mitochondrial import and the N-terminal part housing a “fine-tuning” function. Furthermore, we have constructed a range of point mutations on the GR signal sequence changing positive amino acid residues and stretches of hydrophobic amino acid residues. Overall single mutations had a greater effect on mitochondrial import compared to import into chloroplasts. We have also shown that the recognition of the GR processing site differs between MPP and SPP. Single amino acid substitutions in the vicinity of the processing site clearly affected processing by MPP while processing by SPP showed low sensitivity to single mutations.

Mitochondrial function is dependent upon mitochondrial protein import (MPI), a complex process that transports nuclear-encoded proteins into mitochondria. Little is known about MPI in neurons. We examined the effects of Resveratrol (RSV), a polyphenolic antioxidant compound from grapes, on MPI in a neuronal cell model, differentiated PC12 cells. RSV (50µM, 24h) increased levels of mtGFP, a nuclear encoded mitochondrially targeted green fluorescent protein, and mtHsp70, a physiological mitochondrial heat shock protein, in mitochondria. In addition RSV also increased levels of Tom20, a key translocase of the outer mitochondrial membrane. The RSV mediated increases in mitochondrial proteins were independent of increases in mitochondrial mass or changes in intramitochondrial degradation. RSV also reduced mitochondria membrane potential and decreased basal levels of reactive oxygen species. Taken together, these findings show that RSV increases MPI and that this effect may be an important mechanism in the reported neuroprotective effects of RSV.

Mitochondrial function is dependent upon mitochondrial protein import (MPI), a complex process that transports nuclear-encoded proteins into mitochondria. Little is known about MPI in neurons. We examined the effects of Resveratrol (RSV), a polyphenolic antioxidant compound from grapes, on MPI in a neuronal cell model, differentiated PC12 cells. RSV (50µM, 24h) increased levels of mtGFP, a nuclear encoded mitochondrially targeted green fluorescent protein, and mtHsp70, a physiological mitochondrial heat shock protein, in mitochondria. In addition RSV also increased levels of Tom20, a key translocase of the outer mitochondrial membrane. The RSV mediated increases in mitochondrial proteins were independent of increases in mitochondrial mass or changes in intramitochondrial degradation. RSV also reduced mitochondria membrane potential and decreased basal levels of reactive oxygen species. Taken together, these findings show that RSV increases MPI and that this effect may be an important mechanism in the reported neuroprotective effects of RSV.

The oxidation status of a cell plays a crucial role in aging. As cells get aged, their redox state gets increased. Pex5p is a peroxisomal recycling receptor which binds to newly synthesized cargo proteins in the cytosol and imports them across the peroxisomal membrane. During this transport event, Pex5p gets monoubiquitinated at a conserved cysteine (C11) residue. This C11 is very essential for the recycling of Pex5p from the peroxisomal membrane to back into the cytosol. If the cysteine is replaced by serine, Pex5p does not get recycled back to the cytosol and accumulates on the peroxisomal membrane. In the present study, we have investigated whether the C11 in Pex5p could act as a redox switch. We measured the redox state of the cytosol and the peroxisomal matrix as well as the subcellular localization of catalase in aging cells. We found that an increase in the redox state of peroxisomes (in WT) leads to an increase in the redox state of the cytosol, which ultimately results in the impairment of PTS1 import. Interestingly, in the C11K condition, we did not see an impairment of PTS1 import. These observations support our hypothesis that C11 may act as a redox switch. We also performed some challenging experiments with H2O2. The results of these experiments show that a) import of catalase into peroxisomes sensitizes the cytosol and b) catalase overexpression does have a protective effect against oxidative stress caused by H2O2. In summary the results of our experiments support our hypothesis. However, further evaluation is needed to reveal the precise role of C11 in Pex5p function during cellular aging.

An overview of the theoretical literature for the last two decades suggests that there is no clear-cut relationship one can pin down between exchange rate volatility and trade flows. Analytical results are based on specific assumptions and only hold in certain cases. Especially, the impact of exchange rate volatility on export and import activity investigated separately leads also to dissimilar conclusions among countries studied. The general presumption is that an increase in exchange rate volatility will have an adverse effect on trade flows and consequently, the overall heath of the world economy. However, neither theoretical models nor empirical studies provide us with a definitive answer, leaving obtained results highly ambiguous and inconsistent (Baum and Caglayan, 2006). We purposed to empirically investigate trade effects of exchange rate fluctuations in Sweden from the perspective of export and import in this research. The data comprises period from January 1993 to December 2006, where export and import volumes are considered from the point of their determinants, including exchange rate volatility, which has been measured through EGARCH model. The results for the case of Sweden show that short run dynamics of volatility negatively associated with both export and import, whereas considered from the case of previous period volatility it exhibits positive relationship. These results are consistent with the most findings of prior studies, where the relationship remained ambiguous.

The lentiviral capsid core, which encapsulates the viral RNA genome, is delivered into the target cell cytoplasm during the viral entry process. In the cytoplasm, the conical core undergoes morphological changes, which are termed uncoating. Proper uncoating has been shown to be critical for the infectivity of the lentivirus HIV-1. In addition, the HIV-1 capsid protein is critical for the process of nuclear import of the preintegration complex (PIC). The lentivirus equine infectious anemia virus (EIAV) shares many similarities to HIV-1, including similarities in the capsid protein. In particular, both HIV-1 and EIAV capsid contain a proline-rich loop region in the amino terminal domain of capsid between helices 4 and 5. The host cellular factor cyclophilin A binds this loop in HIV-1 and is critical for proper uncoating. We hypothesized that this helix 4-5 loop was also critical for EIAV infectivity at some early step in the viral infection cycle. We created a panel of amino acid substitution mutations in this loop region. Some of the mutations resulted in severely deleterious effects on EIAV infectivity. Some mutations caused a slight increase in infectivity. The deleterious mutations did not affect uncoating or reverse transcription but appeared to block nuclear import of the PIC. Those mutations in which infectivity was slightly increased did not exhibit significantly different phenotypes from wild-type EIAV at any of the stages examined. The results of this study lend further support to the role of capsid as a determinant of nuclear import and suggest that viral and cellular factors critical to HIV-1 import may also be applicable to EIAV. Future research should focus on identifying the causes of the defects in nuclear import observed for some mutants, as well as attempt to identify the reason for the infectivity increase in others. In addition, inclusion of EIAV in future studies of nuclear import involving HIV-1 can broaden the scope of the data to lentiviruses in general rather than HIV-1 in particular.

I provide evidence on the impact of foreign competition on firms' propensities to engage in mergers and acquisitions. Using import tariff reductions as an exogenous shock that increases foreign industry competition, I find that affected firms are more likely to make acquisitions following a tariff reduction. Cross-sectional tests show that this association is more pronounced for single segment firms, firms that innovate less, or that are more capital intensive, which suggests this association is stronger for firms which stand to gain more from an acquisition. Moreover, the positive relationship between acquisition likelihood and tariff cuts is less pronounced for financially constrained firms and during times of low capital liquidity, which implies that it is easier for firms with greater access to external capital to respond to increases in foreign competition by making acquisitions. Finally, I find that acquisitions made subsequent to tariff decreases are associated with positive wealth gains for bidder shareholders, indicating that these acquisitions are viewed favorably by market participants.

In eukaryotes, the regulation of mRNA translation and decay provides a mechanism which can be finely tuned to control gene expression. This ability to control the life cycle of an mRNA begins with the control of mRNA export from the nucleus and extends to the processes which regulate the degradation of the message. In my work, summarized below, I describe how some of the proteins involved in cytoplasmic decay regulate many aspects of the control of mRNA and also describe a novel regulatory mechanism involving the relocation of cytoplasmic mRNA back into the nucleus of the cell.Firstly, I have identified that the protein Pat1, which has been shown to be critical for translational repression and activation of decapping, consists of essentially 3 major domains. By means of a deletional functional analysis, I show that two of these domains are the primary functional domains responsible for all of the currently ascribed function of Pat1. One domain promotes translational repression and P-body assembly, while the second domain promotes mRNA decapping after assembly of the mRNA into a P-body mRNP. Along with the first evidence that Pat1 binds to RNA, we also determine numerous domain-specific interactions with mRNA decapping factors.In eukaryotic cells mRNAs are produced in the nucleus followed by what is thought to be unidirectional export to the cytoplasm. In the cytosol, mRNAs either associate with ribosomes for translation or can be found in cytoplasmic RNP granules, termed P-bodies, when they are translationally repressed. I have now demonstrated that yeast mRNAs can be re-imported into the nucleus. Import of mRNAs into the nucleus is in competition with translation and increased in strains lacking specific components of cytoplasmic processing bodies, which also exhibit nuclear-cytoplasmic shuttling. This indicates that one function of cytoplasmic granules is to limit the import of cytoplasmic mRNAs back into the nucleus. These results demonstrate a novel pathway for mRNA import into the nucleus and suggest distinct pathways of mRNA export of nascent mRNAs and imported mRNAs.

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This thesis studies the business performance of Thai firms in both domestic and export markets by using the market orientation theoretical framework to explain why some firms are more successful than others. It also investigates how firms become more market-oriented and whether the relationship between market orientation and business performance is moderated by business environment.