The 75 S RNA transcription unit in Balbiani ring 2 and its relation to chromosome structure

Abstract

A defined transcription unit in the Balbiani ring 2 (BR 2) region of chromosome IV in the salivary glands of Chironomus tentans has been characterized on the basis of analysis of the corresponding primary transcript, 75 S RNA, and its functional significance. The available information on the transcription unit and its relation to chromosome structure can be summarized in the following way: 1. The size of the 75 S RNA transcription unit in BR 2 is on the order of 30 000 base pairs. 2. The unit is likely to contain a long coding segment (at least 6000 base pairs), probably corresponding to information for salivary polypeptides. 3. The sequences are distributed in more than one chromomere (probably in 3-5 chromomeres). Further studies are needed before it can be stated whether or not there is a simple one-to-one relation between chromomeres and transcription units in the BR 2 region.