Actin messenger in maternal RNP particles from an insect embryo (Smittia spec., Chironomidae, Diptera).

Actin synthesis was observed in early embryos of the chironomid midgeSmittia spec. The criteria used to identify newly synthesized actin include comigration with purified actin in two-dimensional gel electrophoresis, and peptide mapping after limited proteolysis. Actin was also identified after in vitro translation of RNA or salt washed RNP-particles isolated from newly deposited eggs. While intact RNP-particles stimulated protein synthesis only poorly, the rate of synthesis increased considerably after partial or complete removal of proteins from RNP-particles. Actin was synthesized both during advanced stages of oogenesis and during early embryogenesis. In embryos during intravitelline cleavage actin synthesis was insensitive to inhibitors of transcription (actinomycin D, α-amanitin). Actin was found everywhere along the longitudinal axis of the embryo using a procedure which allowed simultaneous sectioning of a large number of embryos.