ISOLATION AND CDNA CLONING OF A RAT O-6-ALKYLGUANINE-DNA-ALKYLTRANSFERASE GENE, MOLECULAR ANALYSIS OF EXPRESSION IN RAT-LIVER

A rat O6-alkylguanine-DNA-alkyltransferase (ATase) cDNA has been isolated from a rat liver cDNA library by hybridization with the human homologue. The candidate 806 bp cDNA was sequenced and shown to contain a 630 bp open reading frame that could encode a protein of 22.2 kd. Fluorography of labelled ATase indicates a 24 kd protein which is consistent with several previous reports. The derived amino acid sequence demonstrated 81% similarity with the human ATase and 94% identity over a 67 residue region encompassing the putative alkyl acceptor site. Peptide sequences derived from cleaved homogeneous rat ATase have been located in the predicted protein providing additional confirmation of the identity of the cDNA. A 1.05 kb mRNA has been detected in rat liver by Northern analysis; treatment of adult rats with 2-acetylaminofluorene causes an approximately 10-fold induction of this message in liver. Following site directed mutagenesis of the 806 bp cDNA, the 630 bp protein coding sequence has been ligated into an Escherichia coli expression vector to achieve ATase levels of > 3% of total protein in bacterial extracts.