Yeast L double-stranded ribonucleic acid is synthesized during the G1 phase but not the S phase of the cell cycle.
The cytoplasm of Saccharomyces cerevisiae contains two major classes of protein-encapsulated double-stranded ribonucleic acids (dsRNA's), L and M. Replication of L and M dsRNA's was examined in cells arrested in the G1 phase by either alpha-factor, a yeast mating pheromone, or the restrictive temperature for a cell cycle mutant (cdc7). [3H]uracil was added during the arrest periods to cells prelabeled with [14C]uracil, and replication was monitored by determining the ratio of 3H/14C for purified dsRNA's. Like mitochondrial deoxyribonucleic acid, both L and M dsRNA's were synthesized in the G1 arrested cells. The replication of L dsRNA was also examined during the S phase, using cells synchronized in two different ways. Cells containing the cdc7 mutation, treated sequentially with alpha-factor and then the restrictive temperature, enter a synchronous S phase when transferred to permissive temperature. When cells entered the S phase, synthesis of L dsRNA ceased, and little or no synthesis was detected throughout the S phase. Synthesis of L dsRNA was also observed in G1 phase cells isolated from asynchronous cultures by velocity centrifugation. Again, synthesis ceased when cells entered the S phase. These results indicate that L dsRNA replication is under cell cycle control. The control differs from that of mitochondrial deoxyribonucleic acid, which replicates in all phases of the cell cycle, and from that of 2-micron DNA, a multiple-copy plasmid whose replication is confined to the S phase.
Zakian
V A
VA
Hutchinson Cancer Research Center, Division of Genetics, Seattle, Washington 98104, USA.
Wagner
D W
DW
Fangman
W L
WL
D016193:G1 Phase; D012330:RNA, Double-Stranded / Q000096:biosynthesis*; D012331:RNA, Fungal / Q000096:biosynthesis*; D016196:S Phase; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000235:genetics*
D012330:RNA, Double-Stranded; D012331:RNA, Fungal