Intron 1 and the 5'-flanking region of the human thymidylate synthase gene as a regulatory determinant of growth-dependent expression.
We have determined the regulatory regions responsible for the growth-dependent expression of the human thymidylate synthase (TS) gene, using a set of minigenes constructed from segments of the human TS gene and the cDNA clone. Each construct was introduced stably into a TS-negative mutant of rat fibroblast 3Y1 cells. By serum-restricted synchronization of the cloned transformant cells, we found that a minigene with the genomic 5'-flanking region and intron 1 without other introns were sufficient for the normal extent and pattern of S-phase specific expression at the levels of both mRNA and enzymatic activity. In contrast, a TS cDNA clone driven by an SV40-based expression vector showed constitutive expression. Insertion of intron 1 into the cDNA clone in the normal location, or replacement of the viral 5'-promoter region of the cDNA clone by the genomic 5'-flanking sequence converted the constitutive expression to the S-phase dependent one, but only partly, that is, coexistence of the two regions were required for the normal expression. Results obtained by nuclear run-on assay suggested that posttranscriptional controls are also involved in this regulation in consistent with our previous results with the bona fide human TS gene.
Takayanagi
A
A
Laboratory of Mutagenesis, Graduate University for Advanced Studies, Mishima, Japan.
Kaneda
S
S
Ayusawa
D
D
Seno
T
T
D000818:Animals; D015152:Blotting, Northern; D002460:Cell Line; D003001:Cloning, Molecular; D005786:Gene Expression Regulation / Q000235:genetics*; D006801:Humans; D007438:Introns / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D012045:Regulatory Sequences, Nucleic Acid / Q000235:genetics*; D016196:S Phase / Q000235:genetics; D013940:Thymidylate Synthase / Q000235:genetics*
D012333:RNA, Messenger; D013940:Thymidylate Synthase