The basic repeat unit of a Chironomus Balbiani ring gene.

A clone derived from the Balbiani ring b (BRb) gene of Chironomus thummi has been used to study the internal organization of that gene. Much of the gene consists of approximately 80 copies of a ca. 300 bp repeat unit, which are tandemly organized. The BRb clone contains a major part of that unit (242 bp). Sequence analysis shows that approximately 60% of the unit corresponds to short, tandemly organized subsequences, which encode peptides 8 to 11 residues long. In turn, each subsequence consists of even shorter internal repeats, corresponding to a tripeptide (consensus Proline. Serine. Lysine.). The remainder of the ca. 300 bp unit probably does not have obvious repetitive substructure.