Mutagenicity of 5-formyluracil in mammalian cells.

5-Formyluracil, a major oxidized form of thymine, was incorporated into a predetermined site of one of the leading and lagging template strands of a double-stranded vector, and the DNA replication efficiency and the mutation frequency of 5-formyluracil in simian COS-7 cells were investigated. 5-Formyluracil did not block DNA replication and was weakly mutagenic in simian cells. 5-Formyluracil primarily elicited base substitutions at the modified positions.