Figure 2.

arc3 is essential for viability. (A) arc3 null heterozygous diploid cells, arc3Δ/+ (arc3::ura4/⁺), were induced to sporulate. After tetrad dissection, the spores were allowed to grow at 30°C on YEAU plates. Emerged colonies were further examined for autotrophy markers and none were Ura+, indicating that these were arc3⁺ cells. (B) The arc3^nmt mutant cells (strain ARC3NMT), whose arc3 is expressed under the control of the thiamine-repressible nmt promoter, were first treated with (arc3⁻) or without (arc3⁺) 200 nM thiamine to regulate arc3 expression. Time points were taken and identical numbers of cells were spread on MM plates lacking thiamine to measure viability by colony formation (left). (C) WT or arc3^nmt mutant cells were serially diluted and spotted on MM plates contatining 1 nM thiamine and incubated at the indicated temperatures.