The major Rhesus （Rh） protein of the green alga Chlamydomonas reinhardtii, Rhl, is homologous to Rh proteins of humans. It is an integral membrane protein involved in transport of carbon dioxide. To localize a fusio...The major Rhesus （Rh） protein of the green alga Chlamydomonas reinhardtii, Rhl, is homologous to Rh proteins of humans. It is an integral membrane protein involved in transport of carbon dioxide. To localize a fusion of intact Rhl to the green fluorescent protein （GFP）, we used as host a white （Its1） mutant strain of C. reinhardtii, which is blocked at the first step of carotenoid biosynthesis. The Its1 mutant strain accumulated normal amounts of Rhl heterotrophically in the dark and Rhl-GFP was at the periphery of the cell co-localized with the cytoplasmic membrane dye FM4-64. Although Rhl carries a potential chloroplast targeting sequence at its N-terminus, Rhl-GFP was clearly not associated with the chloroplast envelope membrane. Moreover, the N-terminal half of the protein was not imported into chloroplasts in vitro and N-terminal regions of Rhl did not direct import of the small subunit of ribulose bisphosphate carboxylase （SSU）. Despite caveats to this interpretation, which we discuss, current evidence indicates that Rhl is a cytoplasmic membrane protein and that Rhl-GFP is among the first cytoplasmic membrane protein fusions to be obtained in C. reinhardtii. Although Its1 （white） mutant strains cannot be used to localize proteins within sub-compartments of the chloroplast because they lack thylakoid membranes, they should nonetheless be valuable for localizing many GFP fusions in Chlamydomonas.展开更多
Plant viruses are a class of plant pathogens that specialize in movement from cell to cell. As part of their arsenal for infection of plants, every virus encodes a movement protein （MP）, a protein dedicated to enlar...Plant viruses are a class of plant pathogens that specialize in movement from cell to cell. As part of their arsenal for infection of plants, every virus encodes a movement protein （MP）, a protein dedicated to enlarging the pore size of plasmodesmata （PD） and actively transporting the viral nucleic acid into the adjacent cell. As our knowledge of intercellular transport has increased, it has become apparent that viruses must also use an active mechanism to target the virus from their site of replication within the cell to the PD. Just as viruses are too large to fit through an unmodified plasmodesma, they are also too large to be freely diffused through the cytoplasm of the cell. Evidence has accumulated now for the involvement of other categories of viral proteins in intracellular movement in addition to the MP, including viral proteins originally associated with replication or gene expression. In this review, we will discuss the strategies that viruses use for intracellular movement from the replication site to the PD, in particular focusing on the role of host membranes for intracellular transport and the coordinated interactions between virus proteins within cells that are necessary for successful virus spread.展开更多
文摘The major Rhesus （Rh） protein of the green alga Chlamydomonas reinhardtii, Rhl, is homologous to Rh proteins of humans. It is an integral membrane protein involved in transport of carbon dioxide. To localize a fusion of intact Rhl to the green fluorescent protein （GFP）, we used as host a white （Its1） mutant strain of C. reinhardtii, which is blocked at the first step of carotenoid biosynthesis. The Its1 mutant strain accumulated normal amounts of Rhl heterotrophically in the dark and Rhl-GFP was at the periphery of the cell co-localized with the cytoplasmic membrane dye FM4-64. Although Rhl carries a potential chloroplast targeting sequence at its N-terminus, Rhl-GFP was clearly not associated with the chloroplast envelope membrane. Moreover, the N-terminal half of the protein was not imported into chloroplasts in vitro and N-terminal regions of Rhl did not direct import of the small subunit of ribulose bisphosphate carboxylase （SSU）. Despite caveats to this interpretation, which we discuss, current evidence indicates that Rhl is a cytoplasmic membrane protein and that Rhl-GFP is among the first cytoplasmic membrane protein fusions to be obtained in C. reinhardtii. Although Its1 （white） mutant strains cannot be used to localize proteins within sub-compartments of the chloroplast because they lack thylakoid membranes, they should nonetheless be valuable for localizing many GFP fusions in Chlamydomonas.
文摘Plant viruses are a class of plant pathogens that specialize in movement from cell to cell. As part of their arsenal for infection of plants, every virus encodes a movement protein （MP）, a protein dedicated to enlarging the pore size of plasmodesmata （PD） and actively transporting the viral nucleic acid into the adjacent cell. As our knowledge of intercellular transport has increased, it has become apparent that viruses must also use an active mechanism to target the virus from their site of replication within the cell to the PD. Just as viruses are too large to fit through an unmodified plasmodesma, they are also too large to be freely diffused through the cytoplasm of the cell. Evidence has accumulated now for the involvement of other categories of viral proteins in intracellular movement in addition to the MP, including viral proteins originally associated with replication or gene expression. In this review, we will discuss the strategies that viruses use for intracellular movement from the replication site to the PD, in particular focusing on the role of host membranes for intracellular transport and the coordinated interactions between virus proteins within cells that are necessary for successful virus spread.
