IDENTIFICATION OF THE CIS-ELEMENTS REQUIRED FOR TRANSCRIPTIONAL CONTROL OF THE CHINESE-HAMSTER OVARY APRT GENE

Transcriptional regulation of the Chinese hamster ovary (CHO) adenine phosphoribosyltransferase-encoding gene (APRT) was studied. The 5' region of the CHO APRT is G+C-rich, but lacking TATA or CCAAT boxes, RNase protection assays indicate that it contains multiple transcription start points (tsp. A tsp 64 bp upstream from the translation start codon is denoted as +1. Linker-scanning (LS) mutation analysis indicates that the -33 to +19 region is important in regulating APRT transcription, Mutations in the -23 to -14 region abolish transcription initiated from the -23 downstream region. An unidentified protein complex binds to this region, Three Sp1-binding sites are found in the APRT promoter; however, mutations of the Sp1-binding sites do not reduce APRT transcription. Mutations at two putative GCF-binding sites increase levels of transcription.