[Properties of the cell-free protein synthesizing system from the fibroin region of the Bombyx mori silkgland].

Microsomes isolated from the fibroin region of the Bombyx mori silkgland synthesize in the cell-free system a glycin rich polypeptide or polypeptides presumably representing fibroin precursors. Besides microsomes the system requires ATP and ATP-generating system, GTP, soluble protein fraction and tRNA, glycine incorporation is inhibited by puromycin and cycloheximide. It is shown that the synthesis of a polypeptide with high Gly/Lys ratio requires soluble protein fraction isolated from the silk gland at the end of the instar V. When the soluble protein fraction from the larvoe at the early instar V is used the Gly/Lys ratio in the product is markedly lower. These results permit to suggest that fibroin synthesis may be regulated at the level of tRNA aminoacylation.