Genetic interactions of hypomorphic mutations in the m⁷G cap-binding pocket of yeast nuclear cap binding complex: An essential role for Cbc2 in meiosis via splicing of MER3 pre-mRNA

Effects of mutating the Cbc2 cap-binding pocket on yeast growth. (A) The phenotypes of cbc2Δ cells or cbc2Δ tgs1Δ cells harboring CEN LEU2 plasmids with wild-type CBC2 or the indicated mutant alleles were compared by spotting 3-μL aliquots of 10-fold serial dilutions of cells (from liquid cultures grown to mid-log phase at 34°C and adjusted to A₆₀₀ of 0.1) to SD−Leu agar and incubating the plates at the indicated temperatures. Suppression of the tgs1Δ cs phenotype is denoted by ● symbols at right. (B) The growth phenotypes of cbc2Δ and cbc2Δ tgs1Δ cells bearing LEU2 plasmids with the indicated genes were assessed as described in panel A. Suppression of the tgs1Δ cs phenotype is denoted by ◀ symbols at right. The N-terminal amino acid sequence of Cbc2 is shown at the bottom, with the two m⁷G-stacking tyrosines shaded gray and the margins of the N-terminal truncation mutants indicated by arrows.