Abstract
Mouse sarcoma 180 cells have a polypeptide that has the same molecular weight as actin but it is more acidic than α-actin. Its tryptic peptide pattern on reversed-phase HPLC was very similar to that of β+γ-actin, an actin sample prepared by affinity chromatography on DNase I-Sepharose contained the acidic polypeptide, and monoclonal anti-actin antibody reacted with it; therefore, the polypeptide is considered an actin isoform. The mRNA for this variant actin was identified by analyzing the polypeptides translated in vitro, which indicated that the variant actin is not a post-translationally modified form of any known actin. The variant actin was not stained by polyclonal anti-gizzard actin antibody which reacts with γ-cytoplasmic, α-smooth and γ-smooth muscle actins, nor by polyclonal anti-skeletal muscle actin antibody which reacts with skeletal, cardiac and α-smooth muscle actins. These results suggest that this variant actin is related to β-cytoplasmic actin or, is a novel species whose N-terminal amino acid sequence is not Glu-Glu-Glu.
