Specific role in sporulation of the yeast syntaxin Sso1p

The yeast syntaxins Ssolp and Sso2p, acting at the cell membrane in the late secretion pathway, are highly homologous and have redundant functions in mitotically growing haploid and diploid cells. However, when diploid cells undergo sporulation, Ssolp is specifically required (1). This suggests the possible formation of a sporulation-specific complex where Sso2p cannot substitute for Ssolp. We have proceeded to study the role of Ssolp in sporulation. DAPI staining shows that meiosis is completed in sso1/sso1 mutant. The expression of Ssolp and Sso2p during sporulation was monitored in Western blots with antibodies specific for each protein. We found that the levels of both proteins remain constant throughout sporulation. In order to identify the part(s) of Ssolp that are specifically required during sporulation, a number of hybrid constructions between Ssolp and Sso2p were made and tested for their ability to complement the sporulation deficiency of the ssol/ssol strain. Our results suggest that the N-terminal part of Ssolp is particularly important for its sporulation-specific function. 1. Jäntti, J., Aalto. M., Öyen, NI., Sundqvist, L., Keränen, S. and Ronne, H. (2002). J. Cell Sci. 115, 409-420.