Figure 6.

Cig2 B-type cyclin contributes to the inhibition of Cdc18 and DNA replication. (A) The cdc18-K9 temperature-sensitive mutation is rescued by deletion of the cig2⁺ gene. Strains harboring Δcig1, Δcig2, and cdc18-K9 mutations alone or in combinations were tested for their ability to form colonies in YES medium at the restrictive temperature of 35.5°C. The cig1⁺ gene encodes a B-type cyclin of unknown function. The Δcig1 and Δcig2 mutants grow as well as wild-type at 35.5°C. The Δcig1 mutation failed to rescue cdc18-K9. (B) Overexpression of Cig2 inhibits rereplication in cells lacking Cdc13. Cells lacking Cdc13 were obtained by selective germination of spores from strain PR1334 (cdc13::his7⁺/cdc13⁺ ura4⁺/ura4-D18, top) or JLP162 (cdc13:: his7⁺/cdc13⁺ nmt1:cig2⁺(ura4⁺)/ura4-D18, bottom). Rereplication was strongly inhibited by expression of cig2⁺ from the nmt1 promoter. Germinated cells were analyzed by FACS (left) or photographed after staining with DAPI (right). Representative data for cells after 16 h at 32°C are shown.