Fig. 3. (A) Extraction profiles of h1 CaP. Percentage of non-extractable, ectopically expressed h1 CaP constructs in cultured A7r5 smooth muscle cells at three different ionic conditions. The mutant lacking the entire C-terminal tail sequence (h1t) is retained in the cytoskeletal fraction even at higher KCl concentrations compared with the wild-type h1 CaP. Exchanging the tail in h1 CaP for that of either h2 CaP (h1-h2t) or ac. CaP (h1-act) reduces in both cases the amount of CaP present in the cytoskeletal fraction at all three ionic conditions tested. Introduction of the K151N and R156T mutations into the ABS1 of h1 CaP (h1 ABS1-k.o.) also results in a significant reduction of cytoskeletal association. Additional removal of the tail (h1t ABS1-k.o.) restores the levels of this double h1 CaP mutant in the pellet to levels comparable with that of wild-type h1 CaP. (B) Extraction profiles of h2 CaP. Percentage of non-extractable, ectopically expressed h2 CaP constructs in cultured A7r5 smooth muscle cells at three different ionic conditions. Similar to h1 CaP, a mutant lacking the entire C-terminal tail sequence (h2t) increases the amount of CaP present in the cytoskeletal fraction even at higher KCl concentrations compared with the otherwise easily extractable wild-type h2 CaP. Exchanging the tail in h2 CaP for that of either h1 CaP (h2-h1t) or ac. CaP (h2-act) also increases the amount h2 CaP retained in the cytoskeletal fraction, albeit to lower levels. Note that the strongly acidic tail from ac. CaP is less effective than the neutral h1 tail. Mutations of the C-terminal negatively charged residues h2 ch-k.o. neutralize the overall negative character of the tail and result in an extraction profile similar to that for the h2-h1t and h2 t mutants.