Cloning and characterization of a Novikoff hepatoma ribosomal DNA-fragment containing the initiation site of transcription.

A 10.3 kilobase EcoRI fragment of Novikoff hepatoma rat ascites tumor ribosomal gene was cloned in pBR322 vector. The cloned fragment contained part of the 18S RNA gene, and about 8 kilobases of the 5' spacer region. A restriction map was constructed by cleavage of the fragment with BamHI, HindIII, KpnI, PstI, SstI and XhoI enzymes. A putative transcription initiation site for the 45S pre-ribosomal RNA was localized by P1 nuclease protection mapping at a distance of about 130 base pairs 5' to the HindIII site on the restriction map. Both the restriction map and the position of the initiation site of transcription were almost identical to those of the corresponding rat ribosomal DNA fragments.