The Golgi Complex: In Vitro Veritas? Review
Abstract
Understanding thestructure and function of theGolgi comiplex has proved to be among the more challenging probllems in cell biology. The last several years have turned out Ito be particularly exciting in this respect since they have Iyielded new insights and ideas at an increasingly rapid ipace. This period of advance has largely been due to the Idevelopment of powerful new biochemical, morphological, #and genetic approaches to unraveling the complexities of 'this organelle. While much remains to be discovered, the Iproblem now is how to integrate this wealth of information.
'To see if this is possible, we will first summarize how the lslolgi is commonly believed to work and then evaluate the lstrength of the evidence that underlies these views.
iplex has proved to be among the more challenging probllems in cell biology. The last several years have turned out Ito be particularly exciting in this respect since they have Iyielded new insights and ideas at an increasingly rapid ipace. This period of advance has largely been due to the Idevelopment of powerful new biochemical, morphological, #and genetic approaches to unraveling the complexities of 'this organelle. While much remains to be discovered, the Iproblem now is how to integrate this wealth of information.
'To see if this is possible, we will first summarize how the lslolgi is commonly believed to work and then evaluate the lstrength of the evidence that underlies these views.
Present View of the Golgi 'The Golgi complex is essentially a carbohydrate factory. In The first phase is already well under way and has been characterized by a search for essential bits and pieces of the Golgi machinery, a number of which have already been found (NSFlsecl8, aSNAPlsecl7, (J-COP, ARF[Stearnsetal., 19901, rab6p[Goudetal., 1990] ,sec7p [Achstetter et al., 19881, and secl4p [Bankaitis et al., 199Oj) . As we have seen, however, it is at present difficult to know precisely what steps are controlled by each of these components. Nevertheless, the observed conservation of Golgi proteins between S. cerevisiae and mammals is most encouraging for our ability to confirm in living cells the function of components identified in vitro. The combination of cell-free analysis and genetics has proven its worth. The next phase will have to deal with the questions that have arisen. How many Golgi compartments are there? Are compartment boundaries defined by specific protein frameworks? If so, how do they function and how are they regulated? Does transport between Golgi compartments require vesicular carriers? What is the role of tubules? How does the machinery responsible for forward traffic relate to the machinery controlling homotypic fusion? How is specificity of forward and backward traffic regulated? How does lipid composition and organization affect transport? What function does the stack structure have? How do microtubules interact with the Golgi elements? The challenge will be to integrate the information we are now collecting in the context of how the Golgi complex works as a whole.
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