The introduction of CEN14-based plasmids into haploid strains of Saccharomyces cerevisiae resulted in reduced proliferation rates and significantly smaller (20%) cell size than in untransformed control cells. This could be useful to those yeast biotechnology processes that require high levels of gene expression but little or no yeast growth and proliferation. In diploids similar plasmids caused asporogeny, which was possibly a consequence of the reduced cell size.