Mutation spectra of TA*, the major photoproduct of thymidylyl-(3'5')-deoxyadenosine, in Escherichia coli under SOS conditions.
The biological activity of TA*, the major photoproduct of thymidylyl-(3',5')-deoxyadenosine, has remained speculative since it was identified a decade ago. To determine the mutagenicity of TA* in Escherichia coli, we constructed the replicative form of an M13mp18-derived phage containing TA* in the (-)-strand by polymerase-catalyzed elongation of a TA*-containing 49mer opposite a uracil-containing (+)-strand of the phage. The in vitro synthesis mixture was transfected into an ung+, phr- E.coli host and the progeny were screened with a hybridization probe unique for the (-)-strand. TA* was found to block DNA replication substantially in the absence of SOS, but under SOS, TA* was bypassed more efficiently and was highly mutagenic. Among 56 analyzed (-)-strand progeny from two transfections, 46 (82%) were mutants, including six (11%) tandem mutants. The most abundant mutation was a 3'A-->T substitution (31/46, 56%). The possible biological consequences of TA* formation in the highly conserved TATA box consensus sequence on gene expression are discussed in light of the mutagenicity of TA*.
Zhao
X
X
Department of Chemistry, Washington University, St Louis, MO 63130-4899, USA.
Taylor
J S
JS
D017104:Bacteriophage M13; D001435:Bacteriophages / Q000235:genetics; D001483:Base Sequence; D004269:DNA, Bacterial / Q000235:genetics*; D004926:Escherichia coli / Q000235:genetics*; D008969:Molecular Sequence Data; D016296:Mutagenesis; D009692:Nucleic Acid Heteroduplexes; D009838:Oligodeoxyribonucleotides / Q000235:genetics*; D010777:Photochemistry; D013014:SOS Response, Genetics
D004269:DNA, Bacterial; D009692:Nucleic Acid Heteroduplexes; D009838:Oligodeoxyribonucleotides; C042899:deoxythymidylyl-3'-5'-deoxyadenylate