Expression of human cardiac actin in mouse L cells: A sarcomeric actin associates with a nonmuscle cytoskeleton

A cloned human cardiac actin gene, introduced into mouse Ltk^- cells, is expressed in several thymidine kinase (tk)-positive cotransfectants. The clones not only produce authentic polyadenylated human cardiac actin mRNA but also synthesize human cardiac actin protein. The cardiac actin protein, normally found only in myofibrils, is stably accumulated at a high level, about one-third that of the endogenous mouse β-actin. Furthermore, this sarcomeric protein partitions between the Triton X-100 insoluble and soluble phases to the same extent as the endogenous β-actin. This suggests that a sarcomeric actin can participate in the formation of Triton X-100-insoluble cytoskeletal structures.