MRC1-dependent scaling of the budding yeast DNA replication timing program

We describe the DNA replication timing programs of 14 yeast mutants with an extended S phase identified by a novel genome-wide screen. These mutants are associated with the DNA replication machinery, cell-cycle control, and dNTP synthesis and affect different parts of S phase. In 13 of the mutants, origin activation time scales with the duration of S phase. A limited number of origins become inactive in these strains, with inactive origins characterized by small replicons and distributed throughout S phase. In sharp contrast, cells deleted of MRC1, a gene implicated in replication fork stabilization and in the replication checkpoint pathway, maintained wild-type firing times despite over twofold lengthening of S phase. Numerous dormant origins were activated in this mutant. Our data suggest that most perturbations that lengthen S phase affect the entire program of replication timing, rather than a specific subset of origins, maintaining the relative order of origin firing time and delaying firing with relative proportions. Mrc1 emerges as a regulator of this robustness of the replication program

Decreased motility of flagellated microalgae long-term acclimated to CO2-induced acidified waters

Motility plays a critical role in algal survival and reproduction, with implications for aquatic ecosystem stability. However, the effect of elevated CO2 on marine, brackish and freshwater algal motility is unclear. Here we show, using laboratory microscale and field mesoscale experiments, that three typical phytoplankton species had decreased motility with increased CO2. Polar marine Microglena sp., euryhaline Dunaliella salina and freshwater Chlamydomonas reinhardtii were grown under different CO2 concentrations for 5 years. Long-term acclimated Microglena sp. showed substantially decreased photo-responses in all treatments, with a photophobic reaction affecting intracellular calcium concentration. Genes regulating flagellar movement were significantly downregulated (P P D. salina and C. reinhardtii showed similar results, suggesting that motility changes are common across flagellated species. As the flagella structure and bending mechanism are conserved from unicellular organisms to vertebrates, these results suggest that increasing surface water CO2 concentrations may affect flagellated cells from algae to fish