Figure 3.

Effects of insertions immediately downstream of the ³ACUUAC⁸ sequence. The DNA sequences are shown for the 5′ ends of WT U1 and the mutant variants [+1], [+3], etc., named according to the number of nucleotides inserted between positions C⁸ and C⁹. The ³ACTTAC⁸ segment that pairs with the intron 5′SS is highlighted in gray. The [+5], [+10], [+20] and [+30] mutants failed to complement U1Δ in a plasmid shuffle assay and were deemed lethal. The viable U1-[+1] and U1-[+3] strains were spot-tested for growth at the indicated temperatures in parallel with WT cells as per Figure 1B, except that the plates were incubated for 5 d at 25, 20 and 18°C. The synthetic lethal interactions of the U1-[+1] and U1-[+3] mutants are indicated at the bottom of the figure.