Many processes in living cells require
the action of members of the highly diverse class of coiled-coil
proteins. We investigated the localization of open reading frames
within the yeast genome that were predicted to code for
coiled-proteins and that show enhanced transcription during different
stages of meiosis. A number proteins was found that localize either to
the prospore membrane or to the meiotic spindle pole body. Subsequent
analysis allowed us to distinguish several distinct steps governing
the processes of prospore membrane assembly and formation. The
formation of specific precursor membranes starts during meiosis
I. Some of the precursor dock at the SPB during this step. With the
onset of meiosis II, all precursor membranes are relocated to the
SPB. Then, the fusion of these membranes to one continuous membrane
system per SPB takes place. This process requires the function of
meiosis-specific components of the SPB. Thereafter, growth and shaping
of the prospore membrane proceeds, in concert with progression through
meiosis II. We further analyzed the molecular composition of the
meiotic SPB in comparison to its mitotic composition. The results
indicate, that the specific function of the SPB in the assembly
process of the prospore membrane is fulfilled by a special meiosis
specific outer-plaque, the meiotic plaque, which replaces the
mitotic/meiosis I outer-plaque, that is required for cytoplasmic
microtubule organization.
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