Fig. 1. Structure of the Dictyostelium retinoblastoma ortholog rblA with Rb family members from other species. (A) Overview showing blocks of similarity. The gray rectangle N corresponds to the conserved N-terminal region, while blocks A and B are the RbA and RbB domains, respectively. The regions that interact with SP1 and Rb kinase in the human gene are indicated by thin lines. (B,C) Alignment of rblA with Rb proteins from the indicated organisms. Conserved residues are boxed, and identical shaded in gray. (B) The N-terminal region; (C) the RbA and RbB boxes, and the intervening spacer. Black circles indicate positions relevant to the folding of RbA and RbB domains; asterisks indicate amino acids interacting with the LXCXE peptides. (D) Comparison between rblA and human members of the pocket protein family. The scale is the same as in A. The sequences have been arbitrarily aligned at the N-terminal side of the B box.