FIG. 2.

RSK does not phosphorylate FLNb in vitro. (A) Amino acid sequence alignment of a region of human FLNa, FLNb, and FLNc showing the Ser²¹⁵² residue denoted with an asterisk. The residues that lie within the RSK consensus phosphorylation sequence are boxed. Identical residues (black letters on white background), nonconserved residues (white letters on black background), and similar residues (black letters on gray background) are also shown. (B) HEK 293E cells were transfected with HA-tagged RSK-WT. RSK was immunoprecipitated from serum-starved HEK 293E cells (−) or HEK 293E cells that were serum starved and then stimulated with serum (+). Immunoprecipitation was performed with HA antibody. RSK kinase assays were performed as described in the legend to Fig. 1B using recombinant, baculovirus-expressed FLNa or FLNb proteins as substrates.