A calmodulin-like protein (CALP) was purified from wheat embryo by a procedure successively involving precipitation by trichloroacetic acid and chromatography on DEAE-Sephacel, phenyl-Sepharose CL-4B and Ultrogel AcA44. The CALP preparation elutes on gel filtration at a peak elution volume corresponding to a molecular weight of 100 000 and contains two major polypeptides P14 and P16 with molecular weights of 14 000 and 16 000, respectively. P14 and P16 were dissociated, purified by reversed phase HPLC and subjected to amino acid sequencing. The two subunits are structurally distinct, but nevertheless, have a high degree of identity with respect to each other and to acidic ribosomal 'A' proteins from wheat and other eukaryote sources. P14 and P16 both contain amino acid sequences similar to sequences in wheat embryo calmodulin (CaM) and related Ca 2 + -binding proteins. P14, P16 and similar eukaryotic acidic ribosomal 'A' proteins have N-terminal sequences that can be exactly aligned with the second half of CaM. The greatest similarity observed is with sequences of the amphipathic CaM F- and G-helices, the corresponding P14, P16 and ribosomal 'A' protein sequences also having the potential to form amphipathic helices. CALP and the isolated P14 and P16 polypeptides can mimic CaM in reactivating histone-inhibited wheat embryo Ca 2 + -dependent protein kinase. However, CALP does not substitute for CaM in activating avian myosin light chain kinase and does not bind Ca 2 + .