Identification of N-acetylmethionine as the product released during the NH sub(2)-terminal processing of a pseudo-class I actin

Genes for the various isoactins define two classes of actin. Class I actin genes code for Met-Asp(Glu)-actin, and class II actin genes code for Met-X-Asp(Glu)-actin where X is usually cysteine. Using site-directed mutagenesis of a human skeletal muscle isoactin coupled with in vitro transcription and translation methods, the authors have synthesized a pseudoclass I actin in which the penultimate cysteine has been changed to an aspartic acid, thus placing a class I amino terminus on an otherwise class II actin molecule. The results indicate that the major actin determinant controlling differential actin-processing rates is the amino-terminal residue being cleaved, not the remaining structure of the actin molecule.