Multiple alignment of HEAT repeats discussed in the text. For comparison, we also include the 16 HEAT repeats that were detected (and correctly aligned) by our procedures for human importin-β, whose structure is known (Cingolani et al. 1999; pdb code 1QGKA). For each aligned column, conserved residues—elevated with binomial tail probabilities (Neuwald and Green 1994) ofp ≤ .0001—and less conserved, related residues—with tail probabilities of p ≤ .0005—are indicated using an automated hierarchical scheme (Neuwald et al. 1999) as follows: ≥1.25 bits of information, red highlight; 1.25–0.75 bits of information, magenta; ≥70% conserved and hydrophobic, yellow; >66% conserved, black; 50%–66% conserved, dark gray; 33%–50% conserved, black; <33% conserved, dark gray; unconserved, light gray.