Isolation and characterization of a cloned DNA sequence associated with the murine Ah locus and a 3-methylcholanthrene-induced form of cytochrome P -450

Using partially purified mouse liver 23S mRNA known to be associated with theAh locus and 3-methylcholanthrene-induced cytochromeP 1 -450, we synthesized double-stranded cDNA by the successive action of reverse transcriptase (RNA-directed DNA nucleotidyltransferase) and the Klenow A fragment ofEscherichia coli DNA polymerase I. The double-stranded cDNA was inserted into pBR322 plasmid DNA byPst I cleavage and homopolymeric “tailing” and cloned inE. coli LE392. Clone 46 hybridized with [32 P]cDNA made from 23S mRNA from “Ah -responsive” C57BL/6N mice but did not hybridize with similarly prepared [32 P]cDNA from “Ah -nonresponsive” DBA/2N mice. Clone 30 was positive, and clone 7 was negative, with both C57BL/6N and DBA/2N [32 P]cDNA probes; these two clones were therefore used as “positive” and “negative” control clones, respectively. By translation-arrest experiments, clone 46 DNA and clone 30 DNA were shown to be associated with anti-P 1 -450- and anti-albumin-precipitable material, respectively. By agarose gel electrophoresis ofPst I digests, the clone 46 DNA insert was shown to be 1100 base pairs in total length and to contain one internalPst I site. The cDNA made from total mRNA isolated from 3-methylcholanthrene-treated C57BL/6N mice hybridized to the two fragments ofPst I-digested DNA from clone 46, whereas similarly prepared cDNA from 3-methylcholanthrene-treated DBA/2N and control C57BL/6N and DBA/2N mice did not. Of 11 restriction endonucleases used, two (Pst I andXba I) had sites within the clone 46 DNA insert. After hybridization of clone 4632 P-labeled nick-translated DNA toEco RI fragments from A/HeJ mouse genomic DNA and fractionation by RPC-5 chromatography and gel electrophoresis, only one positive band (3-4 kilobase pairs appeared. These data demonstrate conclusively that pBR322 clone 46 DNA is associated with mRNA controlled by the murineAh locus, presumably the structural gene encoding 3-methylcholanthrene-inducedP 1 -450.