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Meiosis is a special form of cell division which results in the formation of haploid cells. At the end of meiosis in yeast four new cells, the so-called spores, are formed inside the boundaries of the mother cell. This morphogenetic process requires de novo formation of the cell membranes. Surprisingly it is the spindle pole bodies (SPBs) which organize the formation of these prospore membranes (PSMs). Membrane vesicles, probably redirected from the secretory pathway, accumulate at the cytoplasmic face of the SPB and fuse to form a continuous membrane system. In our lab we have identified a protein complex which localizes to the tip of this growing membrane, the leading edge protein coat (LEP coat). \nIn this thesis I demonstrate that the S. cereviaiae protein Ssp1p is a novel component of the LEP coat. It is even the most important constituent of the LEP coat as it recruits all other components to this structure. I can show here that Ssp1p is a lipid binding protein and this affinity is probably required for anchoring the protein complex in the membrane. Ssp1p would then act like a hinge, connecting the PSM to Ady3p, another protein of the LEP coat. Deletion of SSP1 results in a block of sporulation. Here I show that this is most probably due to a defect in membrane shaping. In the deletion mutant the PSM sticks very tightly to the nuclear envelope and closes without incorporating cytoplasm. This later on leads to a defect in spore formation and to a loss of viability. One possible explanation for this phenotype would be that the LEP coat serves as a scaffold which provides some structural stability to the membrane while it grows. The protein ring at its tip might also keep the membrane open until all constituents required are enclosed. In addition to its lipid binding activity it is demonstrated that Ssp1p localizes to the plasma membrane of the bud when it is overexpressed in mitotic cells. This is a hint that Ssp1p might be involved in membrane vesicle targeting. Ssp1p could either be directed to target membranes by their lipid composition or by other interacting proteins. As overexpression of Ssp1p in mitotic cells is toxic some interference with the secretory pathway machinery is proposed.