title: A BR 1 gene in Chironomus tentans has a composite structure: a large repetitive core block is separated from a short unrelated 3'-terminal domain by a small intron.
abstract: The large Balbiani ring (BR) genes in the dipteran genus Chironomus have been considered to be homogeneous repetitive structures. Analysis of a genomic DNA segment now reveals that a BR 1 gene in C. tentans is a composite gene, consisting of two different types of sequences. A 15-20 kb core block of tandemly arranged repeat units extends close to the 3' end of the BR 1 gene and ends in repetitive structures partly different from the repeat units in the core block. A 55 bp long intron separates the core block, which probably constitutes a single exon, from a non-related 3'-exon, comprising the final 332 bp of the translated part of the gene. According to hydrophobicity and secondary structure predictions, the 3'-exon encoded peptide is distinctly different from the repetitive core block domain and attains a globular structure. The carboxyl-terminal peptide domain is likely to be a general feature of BR encoded proteins and may have important functions in the excretion and polymerisation of the secretory proteins.
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002683:Chironomidae / Q000235:genetics*; D003001:Cloning, Molecular; D004247:DNA / Q000032:analysis / Q000302:isolation & purification; D004251:DNA Transposable Elements; D004175:Diptera / Q000235:genetics*; D005796:Genes; D007814:Larva; D009693:Nucleic Acid Hybridization; D012091:Repetitive Sequences, Nucleic Acid; D014158:Transcription, Genetic
chemical_list: D004251:DNA Transposable Elements; D004247:DNA