Hybridization of tRNAs of Drosophila melanogaster to the region of the 5S RNA genes of the polytene chromosomes

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Abstract
We have previously reported that four tRNAs of Drosophila melanogaster randomly labeled with iodine-125 hybridize in part to the 56EF region of polytene chromosomes where 5S RNA genes occur. In the presence of a 100-fold excess of unlabeled 5S RNA no hybridization of randomly labeled 125I-tRNAAsp 2γ occurred at 56EF although hybridization elsewhere was not affected. In addition, tRNAAsp 2γ labeled by introducing 125I-5-iodocytidylyl residues into the 3′-CCA end with tRNA nucleotidyl transferase did not hybridize to 56EF but did hybridize to its other sites. The hybridization of tRNALys 2, tRNAGly 3 and tRNAMet 3 at 56EF was not eliminated by a 25 to 100-fold excess of unlabeled 5S RNA. When these tRNAs were labeled at the -CCA terminus they hybridized to 56EF as well as to their other sites with the exception that terminally labeled tRNALys 2 no longer hybridized to 62A. The hybridization of the latter three species of tRNA to the region of the 5S genes, amongst other sites, is confirmed. The previously observed hybridization of tRNAAsp 2γ in this region appears to have been due to contamination of the tRNA sample with traces of material derived from 5S RNA.