Figure 1.

The largest E- and N-gene families in yeast. The family on the left contains no essential genes (N-family), and the family on the right includes two essential members (E-family). The red circles represent essential genes, and the blue squares represent nonessential genes. The E-family represented here consists of various mitochondrial membrane transporters, and the N-family includes seripauperins (poorly characterized multigene family represented, primarily, in subtelomeric regions of yeast chromosomes).