Drosophila and human PCNA are highly similar. (A)Protein sequence alignment of HsPCNA (human), DmPCNA (Drosophila) and ScPCNA (budding yeast). Residues identical to HsPCNA are boxed. Regions in HsPCNA that interact with the PBD of p21  are in red. (B) A conserved PBD in proteins involved in DNA metabolism. Alignment of the PBD from various homologous proteins from different organisms. Accession numbers are indicated in the second column where available. Asterisk denotes the beginning or end of the protein. Identical residues are highlighted in red and conserved substitution in green. (Hs: Homo sapiens; Mm: Mus musculus; Xl: Xenopus laevis; Dm: Drosophila melanogaster; Ce: Caenorhabditis elegans; Sp: Schizosaccharomyces pombe; Sc: Saccharomyces cerevisiae; Mj: Methanococcus jannaschii).