Synthesis and Transport of Myosin in Physarum polycephalum

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Abstract
Immunological techniques were used to study the rate of synthesis and intracellular transport of myosin in the slime mold P. polycephalum. Quantitative precipitation of myosin in homogenates of Physarum was achieved using an antimyosin antibody produced in rabbit in response to purified Physarum myosin. Dodecylsulfate-gel electrophoresis revealed that about 50% of the precipitated material is myosin. The rates of synthesis of total cellular protein and myosin were measured over the mitotic cycle. Both were found to increase exponentially or linearly between 2 successive nuclear divisions. Similarly, no difference in the proportion of myosin-synthesizing polysomes, assayed by precipitation with antimyosin serum, was detected between the S phase and G2 phase of the mitotic cycle. Myosin makes up nearly 2% of total plasmodial proteins. Its transport into the nucleus occurs predominantly during the G2 phase.