Alignment of Saccharomyces SRP21 proteins with C. albicans , N. crassa and S. pombe homologs, metazoan and plant SRP9 proteins as well SRP14 proteins. The alignment of SRP9 to SRP14 is that previously shown in Birse et al . The alignment of SRP9 to SRP21 is based on the results of profile-based searches like the one shown in Fig. 6 and CLUSTALW. The secondary structure from Birse et al. is shown with gray cylinders for α-helices and arrows for β-strands. The region between β-1 and β-2 (box) is not aligned. Boxed residues are basic residues and cysteines protruding from the β-sheet into the solvent, according to Birse et al. Highly conserved residues are shown in dark gray, residues with conservative substitutions having the same physico-chemical properties are shown in light gray. Where organism names are given (Saccharomyces, C. albicans, N. crassa and S. pombe) they refer to the SRP21 proteins identified in this work whereas the SRP9 and SRP14 proteins are denoted by their Swissprot/TREMBL names.