Yir016w (named Sdm1 for deficient in Separation of Daughter and Mother cells) was found in a screen for Saccharomyces cerevisiae cell separation-defective mutants, where yir016w cells were clumped together in groups of three or four. This gene was of special interest due to its ability to interact with Ace2 and members of the RAM (Regulation of Ace2 and Morphogeneis) network, which exert control over cell separation. This study aimed to elucidate the function of this previously uncharacterized gene YIR016W.
The cell separation defect of sdm1 cells was found to be milder than that of RAM mutants, although still of statistical significance. Also, sdm1 cells neither showed the lack of polarization of the RAM mutants, nor any defects in the localization of Cts1, a key chitinase required for cell separation controlled by the transcription factor Ace2. Instead of a role in the RAM network, Sdm1 may play a role in protein trafficking, as sdm1 cells have vacuolar defects.
This study also aimed to localize Sdm1. The protein responsible for Sdm1 expression is Ume6, a key transcriptional regulator of meiosis. While an Sdm1-GFP fusion was not visible under normal growth conditions, under meiosis-inducing conditions the signal was strong enough to be visualized. Using co-localization, Sdm1-GFP was found to be present in the Golgi body, and analysis of sdm1 cells show that they contained defects in the division of their vacuoles. These results point at additional functions of Sdm1, such as the control of mitosis-meiosis switching and protein processing and export.
In addition, a second protein, Yol036w (termed Sdm2) was investigated, as it interacted with both the RAM network and Sdm1. yol036w cells showed no significant phenotypes in our screens, however, its interactions support the idea that it might also be involved in protein trafficking, or in cell wall biogenesis.