No abstract

Fragments from section 3 of the salivary gland X chromosome of D. melanogaster were dissected with a micromanipulator. The DNA was extracted, cut and ligated to a lambda vector in a volume of a few nanoliters in an oil chamber monitored through a microscope. From about 10 pg of DNA we obtained 80 recombinant clones, a sample of which were analysed and shown to contain Drosophila DNA which hybridises in situ to the region of section 3 of the X chromosome. With this technique we can isolate clones from any desired region as small as 200 kb from the euchromatic arms of polytene chromosomes.

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We have analyzed the upstream promoter of the human 7SK RNA gene to determine which protein factors are involved in the transcription of this gene by RNA polymerase III. Using a reconstituted in vitro system, we show directly that octamer binding transcription factors (OTFs) are required for efficient transcription and that they interact with a series of nonconsensus OTF binding sites between positions -70 and -240. The same purified factors that stimulate RNA polymerase II-dependent transcription of the histone H2b gene (OTF-1) and an immunoglobulin light chain gene (OTF-2) also stimulate 7SK transcription by RNA polymerase III. Moreover, OTF-dependent stimulation requires a sequence between positions -48 and -65 that is homologous to the proximal sequence element of the class II snRNA genes. Our findings indicate that some transcription factors are utilized in the transcription of both class II and class III genes.

No abstract