Isolation and partial characterization of a biosynthetic N-terminal methionyl peptide of bovine pars intermedia: relationship to ubiquitin

During in vitro labelling studies of beef pituitary intermediate lobe cells, a 4000 daltons molecular weight peptide was found to be biosynthesized in major yields. The partial amino acid sequence of this peptide has been found to be Met 1, Leu 8, 15 and Lys 6, 11, 27, 29, 33. This partial sequence fits very well the one expected from the N-terminal sequence of bovine and human ubiquitin, a non-histone fragment of the nuclear protein A24. Since an identical peptide was also biosynthesized from rat hypothalamus and mouse AtT-20 tumor cells, the ubiquitous nature of this peptide is further revealed.