The presence of three repeats in the 5' UTR region of thymidylate synthase (TS) is associated with increased TS mRNA expression in cultured human cancer cell lines in vitro.

Thymidylate synthase (TS) gene contains 28-bp polymorphic sequence and 6-bp insert at the 5'- and 3'-untranslated region, respectively. We investigated the role of these two polymorphic traits on TS mRNA expression in nine different cultured human cancer cell lines in vitro. Three cell lines each were 2R/2R, 2R/3R and 3R/3R genotypes. Six of the nine cell lines tested homozygous for the presence of 6-bp insert (+6/+6) and the rest three lacked this insert (-6/-6). TS expression analyses associated homozygous three repeats (3R/3R) to higher TS expression.