Localization of newly synthesized low molecular weight RNA in polytene chromosomes fromChironomus tentans

In salivary glands fromChironomus tentans incubatedin vitro the labeling in the polytene chromosomes of high molecular weight, heterogeneous RNA is selectively inhibited by a substituted benzimidazole (DRB) while low molecular weight RNA remains labelled. The main component of the latter fraction is RNA in the 4–5 S range which has many properties in common with transfer RNA or a precursor to transfer RNA. Inhibited glands display a changed autoradiographic labeling pattern in the chromosomes as compared to controls after administration of tritiated uridinein vitro. The majority of the bands which normally incorporate precursors are not labeled during DRB treatment. The investigation was focussed on chromosome I comprising 30% of the whole genome. Here usually five bands show strong precursor incorporation although all of them are not constantly labeled. A few other bands may also take up label after DRB treatment but less frequently. It is concluded that at least the majority of the bands which are strongly labeled during DRB treatment are likely to contain RNA with properties similar to transfer RNA.