Changes in template activity of protein and globin mRNA during Chironomus development

Abstract

A wheat-germ cell-free protein synthesizing system was established that efficiently translates fourth instar mRNA from Chironomus thummi. The translation products were analyzed by double immunoprecipitation with specific antibodies against Chironomus hemoglobins. The predominant translation products were shown to be globins, comprising about 50% of total protein synthesized. Two globins, globins 2 and 3, which are specific for the fourth instar in vivo, constitute most of the globin produced. The wheatgerm system translates also efficiently total cytoplasmic RNA, purified from animals at successive developmental stages. The kinetics of protein synthesis during development indicate that Chironomus mRNA template activity is low during larval molting and at metamorphosis. RNA from intermolt larvae generally demonstrates high template activity. In the fourth instar two distinct peaks of activity are resolved, one associated with newly molted fourth instars and a second one associated with the prepupal stage. These RNAs direct the synthesis mostly of non-globin proteins. Immunoprecipitation of the translation products shows that globin synthesis is high in intermolt larvae decreasing to very low, or background levels in larvae molting or metamorphosing to pupae. Globins 2 and 3 are synthesized exclusively by newly synthesized globin transcripts in the fourth instar stage. The results show stage-specific translational activity of globin mRNAs during Chironomus development and suggest hormonal control of globin production.