Table II. Effects of GCN4 uORFs in vitro and in vivo.

^aConstructs used for analyses of LUC synthesis in vitro are described in Table I.

^bThe relative amount of LUC produced in reaction mixtures relative to the amount produced by translation of the construct containing no uORFs, which was assigned a value of 100. The average values and the standard errors shown were derived from data representing nine independent experiments employing five different RNA preparations and seven different extract preparations. LUC activity was measured at time-points between 15 and 30 min of incubation, depending on the experiment. The relative order of LUC activities shown here (none >1 >1–4 >1,4 >4) held for all experiments except one, in which RNA containing uORFs 1–4 had similar activity to the construct containing uORF4.

^cThe measurements of ribosomes at the LUC AUG codon were obtained using ImageQuant to analyze the data in Figure 6 lanes 12, 14, 16, 18 and 20), with values normalized as for the LUC assays.

^dThe GCN4–lacZ expression data are from Hinnebusch (1996); expression values were normalized as for the LUC assays.