Fig. 3. Mutations in the polo boxes disrupt Plo1 function in vivo. Diploid strains were constructed in which one copy of plo1⁺ is disrupted by the his3⁺ gene and plo1 mutant gene marked with the ura4⁺ gene is integrated at one of the leu1 loci. The diploids were sporulated and germinated under the selective condition (—His —Ura), which allows the growth of only the plo1 disruptant expressing mutant plo1 genes. Cells were fixed and stained with DAPI. (A) plo1 disruptant cells expressing plo1YQL508AAA. (B) plo1 disruptant cells expressing plo1DHK625AAA. Both types of cells exhibit similar cytological defects to the plo1 disruptant. These defects include mitotic arrest with overcondensed chromosomes (left panels), disorganised septum (middle) and a failure of septation (right). Round cells seen in B are ungerminated spores. Bar, 10 µm.