Genetics, Vol 118, 685-691, Copyright © 1988

INVESTIGATIONS

Bipartite Structure of the 5S Ribosomal Gene Family in a Drosophila melanogaster Strain, and Its Evolutionary Implications

M. L. Samson and M. Wegnez
Present address: Department of Molecular Biology, Massachusetts General Hospital, Boston, Massachusetts 02114.

Knowledge of multigenic family organization should provide insight into their mode of evolution. Accordingly, we characterized the 5S ribosomal gene family in the Drosophila melanogaster strain ry(506). The 5S genes in this strain display a striking HindIII restriction difference compared to the ``standard'' D. melanogaster 5S genes. The sequence of three ry(506) 5S genes was determined. We show that the HindIII restriction site heterogeneity within the ry(506) 5S family most probably results from the same point mutation, suggesting that a single 5S variant was propagated into the 5S cluster of this strain. Furthermore, we demonstrate that the structural organization of the 5S genes in ry(506) is a bipartite structure, i.e., that about 40% of the 5S genes constitute a HindIII(+)/HindIII(-) mixed cluster, while those remaining constitute an homogeneous HindIII(-) cluster. The events which might lead to such an heterogeneous pattern are discussed from an evolutionary point of view.

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