Figure 4.

Phenotypic effects of deletion or over-expression of Orp4 protein. (A and B) Deletion of Orp4. Spores from a control diploid strain (ura4⁺/ura4-D18) or a diploid strain in which one copy of the orp4⁺ gene replaced by the ura4⁺ gene (ura4-D18/ura4-D18 orp4⁺/orp4∷ura4⁺) were incubated in medium lacking uracil for 15 hr and stained with DAPI. The control spores yielded a population of growing vegetative cells with mostly normal morphology (A). Spores lacking the orp4⁺ gene yielded a variety of terminal phenotypes, including elongated cells with abnormal nuclei (n) and “cut” cells (c) with the septum separating unequal nuclear masses (B). An ungerminated spore is marked by (s). (C–F) Over-expression of Orp4 protein or its domains. Wild-type Sc. pombe cells were transformed with vector alone (C) or with plasmids expressing the N-terminal domain of Orp4p (D), the C-terminal domain of Orp4p (E) or the complete Orp4p (F) under the control of the inducible nmt1⁺ promoter. Twenty hours after induction the cells were fixed and stained with DAPI. Approximately 30% of cells over-expressing the N-terminal domain of Orp4p contained a septum with a single nucleus (D). Arrows indicate septa. The majority of cells over-expressing the C-terminal domain of Orp4p were elongated and many exhibited abnormal nuclear morphology (E). Cells over-expressing the complete Orp4p showed both phenotypes (F).