[Abnormal expression of isoactin genes]

Cytoplasmic isoactins of mouse fibroblast L-cells were examined by two-dimensional gel electrophoresis. In contrast to other cultured cell lines, which contain both beta- and gamma-actins. L-cells contained only beta-actin species. When RNA of L-cells were translated in a nuclease-treated reticulocyte lysate system, actin synthesized in vitro also appeared as only beta-actin. After digestion of genomic DNAs of both L-cells and mouse brain, which contains beta- and gamma-actins, by Eco RI, Hind III, Bam HI and Sal I, obtained fragments were investigated by Southern blott analysis using 32P -labeled probe constructed from PA1 which carries a full length copy of chicken beta-actin mRNA. No differences in the patterns were detected between L-cell and brain DNAs. This result suggests that the absence of gamma-actin expression in L-cells is not due to gross deletions, insertions or rearrangements of isoactin genes. However, the use of the isoschizomeric pair of restriction enzymes, Hpa II and Msp I, resulted in different patterns of isoactin genes, implying a possible involvement of methylation in regulation of isoactin gene expression.