Sequences translated by Balbiani ring 75S RNA in vitro are present in giant secretory protein from Chironomus tentans.

The 75S RNA originating in the large Balbiani rings 1 and 2 (BR1 and 2) was isolated and used for in vitro translation in the mRNA dependent reticulocyte lysate. Conditions (K+-concentration, temperature, time etc), were optimized for obtaining translation products of maximal size. Polypeptide chains up to about 500,000 D were obtained but no complete translation products. Tryptic fingerprints were performed on the in vitro products as well as on the secretory protein components nos. I and II+III labelled with 35S-methionine. There was a large degree of correspondence between the fingerprint of the in vitro product and that of component I but less to that of component II+III. The results suggest that 75S RNA with an origin in the BR1 and BR2 codes for the giant secretory protein component I.