Saccharomyces cerevisiae, physiological studies have previously shown the presence of an active u... more Saccharomyces cerevisiae, physiological studies have previously shown the presence of an active uptake system driven by electrogenic proton symport. We have used transposon mutagenesis to isolate mutants affected in the transport of glycerol into the cell. Here we present the identification of YGL084c, encoding a multi-membrane-spanning protein, as being essential for proton symport of glycerol into Saccharomyces cerevisiae. The gene is named GUP1 (Glycerol UPtake) and is important for growth on glycerol as carbon and energy source, as well as for osmotic protection by added glycerol, of a strain deficient in glycerol production. Another ORF, YPL189w, presenting a high degree of homology to YGL084c, similarly appears to be involved in active glycerol uptake in salt-containing glucose-based media in strains deficient in glycerol production. Analogously, this gene is named GUP2. To our knowledge, this is the first report on a gene product involved in active transport of glycerol in yeasts. Mutations with the same phenotypes occurred in two other open reading frames of previously unknown function, YDL074c and YPL180w.
Glycerol and other polyols are used as osmoprotectants by many organisms. Several yeasts and othe... more Glycerol and other polyols are used as osmoprotectants by many organisms. Several yeasts and other fungi can take up glycerol by proton symport. To identify genes involved in active glycerol uptake in Saccharomyces cerevisiae we screened a deletion mutant collection comprising 321 genes encoding proteins with 6 or more predicted transmembrane domains for impaired growth on glycerol medium. Deletion of STL1, which encodes a member of the sugar transporter family, eliminates active glycerol transport. Stl1p is present in the plasma membrane in S. cerevisiae during conditions where glycerol symport is functional. Both the Stl1 protein and the active glycerol transport are subject to glucose-induced inactivation, following identical patterns. Furthermore, the Stl1 protein and the glycerol symporter activity are strongly but transiently induced when cells are subjected to osmotic shock. STL1 was heterologously expressed in Schizosaccharomyces pombe, a yeast that does not contain its own active glycerol transport system. In S. pombe, STL1 conferred the ability to take up glycerol against a concentration gradient in a proton motive force-dependent manner. We conclude that the glycerol proton symporter in S. cerevisiae is encoded by STL1.
Abstract Although some browsers, such as Netscape, already o er some support for operation under ... more Abstract Although some browsers, such as Netscape, already o er some support for operation under low bandwidth connections, present WWW navigation tools are still unsuited for mobile environments. When bandwidth is low and connection time is ...
Total order multicast greatly simplifies the implementation of fault-tolerant services using the ... more Total order multicast greatly simplifies the implementation of fault-tolerant services using the replicated state machine approach. The additional latency of total ordering can be masked by taking advantage of spontaneous ordering observed in LANs: A tentative delivery allows the application to proceed in parallel with the ordering protocol. The effectiveness of the technique rests on the optimistic assumption that a large share of correctly ordered tentative deliveries offsets the cost of undoing the effect of mistakes. This paper proposes a simple technique which enables the usage of optimistic delivery also in WANs with much larger transmission delays where the optimistic assumption does not normally hold. Our proposal exploits local clocks and the stability of network delays to reduce the mistakes in the ordering of tentative deliveries. An experimental evaluation of a modified sequencer-based protocol is presented, illustrating the usefulness of the approach in fault-tolerant database management.
Semantic Reliability is a novel correctness criterion for multicast protocols based on the concep... more Semantic Reliability is a novel correctness criterion for multicast protocols based on the concept of message obsolescence: A message becomes obsolete when its content or purpose is superseded by a subsequent message. By exploiting obsolescence, a reliable multicast protocol may drop irrelevant messages to find additional buffer space for new messages. This makes the multicast protocol more resilient to transient performance perturbations of group members, thus improving throughput stability. This paper describes our experience in developing a suite of semantically reliable protocols. It summarizes the motivation, definition and algorithmic issues and presents performance figures obtained with a running implementation. The data obtained experimentally is compared with analytic and simulation models. This comparison allows us to confirm the validity of these models and the usefulness of the approach. Finally, the paper reports the application of our prototype to distributed multi-player games.
Traditional broadcast protocols fail to scale to large settings. Several recent attempts have pro... more Traditional broadcast protocols fail to scale to large settings. Several recent attempts have proven efficient to ensure reliable information dissemination in groups composed of a large number of participants. This paper proposes a reliable multicast protocol that integrates two complementary approaches to deal with the large-scale dimension in group communication protocols: gossip-based probabilistic and semantic-based protocols.
Epidemic, or probabilistic, multicast protocols have emerged as a viable mechanism to circumvent ... more Epidemic, or probabilistic, multicast protocols have emerged as a viable mechanism to circumvent the scalability problems of reliable multicast protocols. However, most existing epidemic approaches use connectionless transport protocols to exchange messages and rely on the intrinsic robustness of the epidemic dissemination to mask network omissions. Unfortunately, such an approach is not networkfriendly, since the epidemic protocol makes no effort to reduce the load imposed on the network when the system is congested.
Os acórdãos, as ementas, o artigo e as informações contidos na presente edição foram obtidos em p... more Os acórdãos, as ementas, o artigo e as informações contidos na presente edição foram obtidos em páginas da "internet" ou enviados pelos seus prolatores para a Comissão da Revista e Outras Publicações do Tribunal Regional do Trabalho da 4ª Região. Por razões de ordem prática, alguns deles foram editados e não constam na íntegra.
Saccharomyces cerevisiae, physiological studies have previously shown the presence of an active u... more Saccharomyces cerevisiae, physiological studies have previously shown the presence of an active uptake system driven by electrogenic proton symport. We have used transposon mutagenesis to isolate mutants affected in the transport of glycerol into the cell. Here we present the identification of YGL084c, encoding a multi-membrane-spanning protein, as being essential for proton symport of glycerol into Saccharomyces cerevisiae. The gene is named GUP1 (Glycerol UPtake) and is important for growth on glycerol as carbon and energy source, as well as for osmotic protection by added glycerol, of a strain deficient in glycerol production. Another ORF, YPL189w, presenting a high degree of homology to YGL084c, similarly appears to be involved in active glycerol uptake in salt-containing glucose-based media in strains deficient in glycerol production. Analogously, this gene is named GUP2. To our knowledge, this is the first report on a gene product involved in active transport of glycerol in yeasts. Mutations with the same phenotypes occurred in two other open reading frames of previously unknown function, YDL074c and YPL180w.
Glycerol and other polyols are used as osmoprotectants by many organisms. Several yeasts and othe... more Glycerol and other polyols are used as osmoprotectants by many organisms. Several yeasts and other fungi can take up glycerol by proton symport. To identify genes involved in active glycerol uptake in Saccharomyces cerevisiae we screened a deletion mutant collection comprising 321 genes encoding proteins with 6 or more predicted transmembrane domains for impaired growth on glycerol medium. Deletion of STL1, which encodes a member of the sugar transporter family, eliminates active glycerol transport. Stl1p is present in the plasma membrane in S. cerevisiae during conditions where glycerol symport is functional. Both the Stl1 protein and the active glycerol transport are subject to glucose-induced inactivation, following identical patterns. Furthermore, the Stl1 protein and the glycerol symporter activity are strongly but transiently induced when cells are subjected to osmotic shock. STL1 was heterologously expressed in Schizosaccharomyces pombe, a yeast that does not contain its own active glycerol transport system. In S. pombe, STL1 conferred the ability to take up glycerol against a concentration gradient in a proton motive force-dependent manner. We conclude that the glycerol proton symporter in S. cerevisiae is encoded by STL1.
Abstract Although some browsers, such as Netscape, already o er some support for operation under ... more Abstract Although some browsers, such as Netscape, already o er some support for operation under low bandwidth connections, present WWW navigation tools are still unsuited for mobile environments. When bandwidth is low and connection time is ...
Total order multicast greatly simplifies the implementation of fault-tolerant services using the ... more Total order multicast greatly simplifies the implementation of fault-tolerant services using the replicated state machine approach. The additional latency of total ordering can be masked by taking advantage of spontaneous ordering observed in LANs: A tentative delivery allows the application to proceed in parallel with the ordering protocol. The effectiveness of the technique rests on the optimistic assumption that a large share of correctly ordered tentative deliveries offsets the cost of undoing the effect of mistakes. This paper proposes a simple technique which enables the usage of optimistic delivery also in WANs with much larger transmission delays where the optimistic assumption does not normally hold. Our proposal exploits local clocks and the stability of network delays to reduce the mistakes in the ordering of tentative deliveries. An experimental evaluation of a modified sequencer-based protocol is presented, illustrating the usefulness of the approach in fault-tolerant database management.
Semantic Reliability is a novel correctness criterion for multicast protocols based on the concep... more Semantic Reliability is a novel correctness criterion for multicast protocols based on the concept of message obsolescence: A message becomes obsolete when its content or purpose is superseded by a subsequent message. By exploiting obsolescence, a reliable multicast protocol may drop irrelevant messages to find additional buffer space for new messages. This makes the multicast protocol more resilient to transient performance perturbations of group members, thus improving throughput stability. This paper describes our experience in developing a suite of semantically reliable protocols. It summarizes the motivation, definition and algorithmic issues and presents performance figures obtained with a running implementation. The data obtained experimentally is compared with analytic and simulation models. This comparison allows us to confirm the validity of these models and the usefulness of the approach. Finally, the paper reports the application of our prototype to distributed multi-player games.
Traditional broadcast protocols fail to scale to large settings. Several recent attempts have pro... more Traditional broadcast protocols fail to scale to large settings. Several recent attempts have proven efficient to ensure reliable information dissemination in groups composed of a large number of participants. This paper proposes a reliable multicast protocol that integrates two complementary approaches to deal with the large-scale dimension in group communication protocols: gossip-based probabilistic and semantic-based protocols.
Epidemic, or probabilistic, multicast protocols have emerged as a viable mechanism to circumvent ... more Epidemic, or probabilistic, multicast protocols have emerged as a viable mechanism to circumvent the scalability problems of reliable multicast protocols. However, most existing epidemic approaches use connectionless transport protocols to exchange messages and rely on the intrinsic robustness of the epidemic dissemination to mask network omissions. Unfortunately, such an approach is not networkfriendly, since the epidemic protocol makes no effort to reduce the load imposed on the network when the system is congested.
Os acórdãos, as ementas, o artigo e as informações contidos na presente edição foram obtidos em p... more Os acórdãos, as ementas, o artigo e as informações contidos na presente edição foram obtidos em páginas da "internet" ou enviados pelos seus prolatores para a Comissão da Revista e Outras Publicações do Tribunal Regional do Trabalho da 4ª Região. Por razões de ordem prática, alguns deles foram editados e não constam na íntegra.
Uploads
Papers by Rui Oliveira