Disease relevance of 28SrRNA:CR40459

• Drosophila rDNA units that have an interruption in the 28S rRNA coding region are not transcribed in vivo, but restriction digests of a recombinant phage DNA that contains such a unit are active as template for in vitro rDNA transcription [1].

High impact information on 28SrRNA:CR40459

• We describe a cloned segment of D. melanogaster DNA (cDm219) that contains five tandemly arranged sequence units homologous to the type I insertion sequence found in the majority of 28S rRNA genes on the X chromosome [2].
• The basic repeating unit of the rRNA gene consists of a segment coding for 18S rRNA and 28S rRNA followed by a non-transcribed spacer (Fig.1) [3].
• We have determined the nucleotide sequence of the initiation region in four cloned ribosomal genes from D. melanogaster which are not interrupted and in four cloned ribosomal genes in which the 28S rRNA coding region is interrupted by a 5-kilobase type 1 insertion [4].
• The interband chromosome regions that are immediately distal or proximal to the 18/28S rRNA locus have been involved in a disproportionately large number of natural inversion breaks observed in the euchromatic portion of the polytene chromosome [5].
• R2 is a non-long terminal repeat retrotransposable element that inserts itself site specifically in the 28S rRNA genes of arthropods [6].

Biological context of 28SrRNA:CR40459

• In Drosophila melanogaster, the multiply repeated genes encoding 18S and 28S rRNA are located on the X and Y chromosomes [7].
• Most repeat units of rDNA in Drosophila virilis are interrupted in the 28S rRNA coding region by an intervening sequence about 10 kb in length; uninterrupted repeats have a length of about 11 kb [8].
• This corresponds to a variable stem region previously identified in eukaryotic 28S rRNA at a site analogous to the L1 ribosomal protein binding site of prokaryotic 23S rRNA (27) [9].
• The 70 novel compensatory mutations identified in the 28S rRNA show a strong (70%) bias toward A-U base pairs, suggesting that a process of biased mutation and/or biased fixation of A and T point mutations or AT-rich slippage-generated motifs has occurred during the evolution of D. melanogaster rDNA [10].
• In Drosophila melanogaster the tandemly arranged repetitive sequences coding for 18S and 28S rRNA are heterogenous at the level of the spacers between units and insertions that interrupt many 28S rRNA genes [11].

References