ANALYSIS OF THE MAMMALIAN GADD45 GENE AND ITS RESPONSE TO DNA-DAMAGE

The gadd45 gene is transcriptionally activated through at least two di fferent mechanisms; one following treatment with base-damaging agents such as methylmethane sulfonate and UV radiation and the other followi ng ionizing radiation. To investigate the sequences involved in induct ion of gadd45 by agents producing high levels of base damage, the hams ter, human, and mouse genes were sequenced. Comparison of these sequen ces revealed a high level of conservation between species of 1500 base pairs of the proximal promoter and 700 base pairs within the third in tron. However, in the promoter regions, there was no conservation betw een species of any transcription factor binding sites known to confer DNA damage responsiveness. The promoter of the hamster gene was induci ble by base-damaging agents in both rodent and human cell lines and th e human gene was inducible in a rodent cell line. This indicates that both sequence elements in the gadd45 promoter and factors binding to t hese sites are conserved in mammalian cells. Deletion analysis of the hamster promoter did not reveal any specific sequence which conferred damage inducibility and the maximal response required a large portion of the promoter. The hamster promoter was not inducible by ionizing ra diation, suggesting that sequences outside the promoter region used, s uch as a p53 binding site in the third intron, are necessary. The huma n GADD45 gene was mapped to chromosome 1p31.1-31.2.