Table 2.

Relative rates of RNA synthesis in the spt4Δ and WT strains

Strain	[3H]uridine incorporation (a)	Sp. act. of UTP (b)	Synthesis rate (a)/(b)
WT	1.0	1.0	1.0
spt4Δ	0.45 ± 0.05	0.65 ± 0.06	0.69 ± 0.10

NOY388 (WT) and NOY2167 (spt4Δ), each carrying pRS316 (to make cells Ura⁺), were grown in SD-Ura at 30°C to A₆₀₀ = ≈0.3. Cells were pulse-labeled with [³H]uridine for 5 min, and incorporation of [³H]uridine into TCA-precipitable total RNA fraction was measured. Three independent cultures were used for each strain, and the average value was calculated for the rate of incorporation in the spt4Δ relative to WT strains. Under the same experimental conditions, specific activities (Sp. act.) of ³H-labeled UTP were measured for each strain by using steady-state labeling of pool UTP with [³²P]- and [³H]uridine pulse-labeling for 2.5, 5, and 10 min (see Supporting Materials and Methods). Sp. act. were approximately the same at these three time points for each of the strains. Averages of the values for 2.5 and 5 min were used as average Sp. act. of UTP during the 5-min pulse-labeling, and the data from two independent experiments were used to calculate the relative Sp. act. shown in the table. The relative total RNA synthesis rate in the spt4Δ was then calculated from the incorporation data corrected for the difference in pool UTP Sp. act. between the two strains.