INDUCTION OF THE MOUSE RIBONUCLEOTIDE REDUCTASE R1 AND R2 GENES IN RESPONSE TO DNA-DAMAGE BY UV-LIGHT

Ribonucleotide reductase is responsible for the production of deoxyrib onucleotides required for DNA synthesis and consists of two nonidentic al subunits, proteins R1 and R2. Here we show that the R1 promoter can be induced up to 3-fold, and the R2 promoter is induced up to 10-fold by UV light in a dose-dependent manner. This was demonstrated using s erum-starved, synchronized G(0)/G(1) mouse fibroblast 3T3 cells stably transformed with different R1 and R2 promoter-luciferase reporter gen e constructs, R2 promoter activation requires a minimal promoter, cont aining a TTTAAA element plus the transcription start, and either three upstream DNA-protein binding regions or one proximal, NF-Y binding re gion. This is different from proliferation-specific activation of the R2 promoter. Using Northern blotting we show a preferential accumulati on of the minor, 1.6-kilobase R2 transcript in irradiated cells, where as the levels of the major 2.1-kilobase transcript are unchanged. No R 2 promoter activation was observed after treatment of mouse cells with agents reported to induce the ribonucleotide reductase genes in Sacch aromyces cerevisiae such as hydroxyurea or methylmethane sulfonate. Th is indicates that activation of ribonucleotide reductase gene expressi on is specific for nucleotide excision repair in mammalian cells and n ot part of a general response to DNA damage.