FIGURE 1:

Multiple species of the N-terminal product of CREB-H due to phosphorylation. (a) Schematic indicating the conserved bZip and transmembrane (TM) domains, the S1P and S2P cleavage sites (x), and the mature cleaved product, termed CREB-HΔTMC. (b) Western blot showing CREB-HΔTMC after transfection in COS cells, migrating as multiple species (lane 1), which comigrate with those produced by brefeldin A (BFA)–induced cleavage of the full-length (FL) precursor form (lane 3), as discussed in the text. (c) Soluble extracts of cells expressing CREB-HΔTMC were treated with λ phosphatase for increasing times at 37°C (0, 2, 5, 7, 10, 15, 30 min; lanes 3–9) or as controls, without phosphatase (lane 1) or with phosphatase in the presence of phosphatase inhibitors (10 mM sodium orthovanadate and 20 mM NaF; lane 2). Phosphatase treatment converts the upper form, N¹, to the N form, with species likely representing multiple phosphorylated forms (small arrows) closely migrating between N and N¹.