FIG. 2.

Splicing defects caused by U2-G53A are suppressed or enhanced by different CUS2 alleles. Yeast strains carrying the indicated alleles of U2 and CUS2 were grown at 30°C and shifted to 18°C for 4 h before extraction of RNA and primer extension with a labeled oligonucleotide complementary to U3 snRNA. Samples were normalized to contain the same amount of spliced U3 so that the level of unspliced U3 indicates splicing inhibition. Lane 1, U2-G53A with cus2::HIS3; lane 2, U2-G53A with CUS2⁺; lane 3, U2-G53A with CUS2-9; lane 4, U2-G53A with CUS2-25; lane 5, wild-type U2 with cus2::HIS3; lane 6, wild-type U2 with CUS2⁺.