Multiple sequence alignment of human PCI subunits from proteasome lid, CSN and eIF3. Shown are only the segments matched by the PROSITE PCI domain. Conserved residues printed on black background were found in at last 50 % of ~60 PCI proteins from selected species, from which only human representatives are shown. Grey background was assigned to positions occupied by residues with similar physicochemical properties in at least 50 % of the sequences. The alignment was shaded using BOXSHADE http://www.ch.embnet.org/software/BOX_form.html. Above the PCI alignment secondary structure prediction as calculated from JPred  is presented. In these calculations sequences of eIF3k homologues were not included. Secondary structure elements of eIF3k as derived from PDB structure 1RZ4 are shown in a separate row. The abbreviations denote the following secondary structure types: E extended (sheet) and H helix. In addition, structural subdomain classification ('HAM', 'WH') as described in Wei et al.  and domain boundaries according to PCI profiles from PROSITE and Pfam are provided. Sequence names correspond to the following SwissProt database entries: eIF3k (Q9UBQ5), PSMD3 (O43242), PSMD6 (Q15008), PSMD8 (P48556), PSMD11 (O00231), PSMD12 (O00232), PSMD13 (Q9UNM6), CSN1 (Q13098), CSN2 (P61201), CSN3 (Q9UNS2), CSN4 (Q9BT78), CSN8 (Q99627).