MYOSIN SYNTHESIS IN EMBRYONIC CHICKEN FIBROBLASTS

The rate of constitutive myosin synthesis was measured in cultures of replicating embryonic chicken skin fibroblasts by pulse labeling with [3H]leucine. These cells synthesized the 200,000-dalton heavy chain of myosin (MHC) at a rate of 3.2x103 molecules/cell/min. Additionally, an independent estimate of the MHC synthesis rate needed to maintain a constant level of constitutive MHC/cell was calculated from total protein content, percentage MHC, fibroblast doubling time, and MHC half-life. This calculated rate of ~2.9x103 molecules/cell/min was in close agreement with the measured rate. By comparison, the synthesis rate of myofibrillar MHC in fully activated muscle cell cultures was ~2.9x104 molecules/nucleus/min.