Cell-Free translation of Balbiani ring RNA (75S) ofChironomus tentans salivary glands into high molecular weight products

Summary Cell-free translation of salivary gland RNA or of purified Balbiani ring RNA (75S) in a reticulocyte lysate system gives rise to high molecular weight translational products (HMTP). In addition to a common size (approx. 1×10⁶ daltons) HMTP share imunogenic determinants with the giant secretory proteins of salivary glands. This suggests that HMTP correspond to in vivo secreted proteins and thus, corroborates the notion that 75S-RNA is the messenger for these proteins. The time course of HMTP synthesis and the lack of appearance of lower molecular weight components as translational products of 75S-RNA indicate that the synthesis of HMTP (and of secretory proteins) occurs in one piece by an uninterrupted process. HMTP are regarded the largest polypeptides so far synthesized in a cell-free system.