FIG. 2.

Ras^V12 induces phosphorylation on serine 64 of C/EBPβ. (A) HPLC fractions encompassing Ras^V12-induced peak 4 (Fig. 1) were pooled and subjected to Edman degradation. The label released at each sequencing cycle was quantitated by phosphorimaging. The N-terminal sequence of a candidate tryptic peptide (amino acids 60 to 101) containing serine at position 5 (labeled with an asterisk) is shown in the inset. (B) Wild-type and mutant (S64A) C/EBPβ proteins were expressed in L cells without (−) or with (+) Ras^V12, labeled with ³²P, and immunoprecipitated as described for Fig. 1. (C) Samples from panel B (wild-type C/EBPβ + Ras and S64A C/EBPβ + Ras) were subjected to tryptic digestion and reverse-phase HPLC.