Cell
Volume 14, Issue 2, June 1978, Pages 269-278
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Article
X and Y chromosomal ribosomal DNA of drosophila: comparison of spacers and insertions

https://doi.org/10.1016/0092-8674(78)90113-7Get rights and content

Abstract

In Drosophila melanogaster, the genes coding for 18S and 28S ribosomal RNA (rDNA) are clustered at one locus each on the X and the Y chromosomes. We have compared the structure of rDNA at the two loci. The 18S and 28S rRNAs coded by the X and Y chromosomes are very similar and probably identical (Maden and Tartof, 1974). In D. melanogaster, many rDNA repeating units are interrupted in the 28S RNA sequence by a DNA region called the insertion. There are at least two sequence types of insertions. Type 1 insertions include the most abundant 5 kilobase (kb) class and homologous small (0.5 and 1 kb) insertions. Most insertions between 1.5 and 4 kb have no homology to the 5 kb class and are identified as type 2 insertions. In X rDNA, about 49% of all rDNA repeats have type 1 insertions, and another 16% have type 2 insertions. On the Y chromosome, only 16% of all rDNA repeats are interrupted, and most if not all insertions are of type 2.

rDNA fragments derived from the X and Y chromosomes have been cloned in E. coli. The homology between the nontranscribed spacers in X and Y rDNA was studied with cloned fragments. Stable heteroduplexes were found which showed that these regions on the two chromosomes are very similar.

The evolution of rDNA in D. melanogaster might involve genetic exchange between the X and Y chromosomal clusters with restrictions on the movement of type 1 insertions to the Y chromosome.

References (33)

  • H. Wallace et al.

    Ribosomal cistrons and the nucleolar organizer

    Biochim. Biophys. Acta

    (1966)
  • P.K. Wellauer et al.

    The structural organization of ribosomal DNA in Drosophila melanogaster

    Cell

    (1977)
  • P.K. Wellauer et al.

    The molecular basis for length heterogeneity in ribosomal DNA from Xenopus laevis

    J. Mol. Biol.

    (1976)
  • P.K. Wellauer et al.

    The arrangement of length heterogeneity in repeating units of ribosomal DNA from Xenopus laevis

    J. Mol. Biol.

    (1976)
  • R.L. White et al.

    R loop mapping of the 18S and 28S sequences in the long and short repeating units of Drosophila melanogaster rDNA

    Cell

    (1977)
  • H.J. Barr et al.

    The development and cytology of Drosophila embryos genetically deficient for nucleolar organizers

    J. Cell Biol.

    (1970)
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