Inhibition of DNA replication with hydroxyurea during thymine starvation of Escherichia coli shows that active DNA synthesis is not required for thymineless death (TLD). Hydroxyurea experiments and thymine starvation of lexA3 and uvrA DNA repair mutants rule out unbalanced growth, the SOS response, and nucleotide excision repair as explanations for TLD.

The interference of platelets with the estimation of unsched uled DNA synthesis in human peripheral mononuclear leukocytes following genotoxic exposure was studied. A 96% reduction in the unscheduled DNA synthesis value was achieved by incubat ing [3H]thymidine with platelet-rich plasma for 5 hr at 37°.Using radioactive thymine-containing compounds, together with quan titative analyses based o...

The dynamics of electron attachment to the DNA base thymine are investigated using femtosecond time-resolved photoelectron imaging of the gas phase iodide-thymine (I(-)T) complex. An ultraviolet pump pulse ejects an electron from the iodide and prepares an iodine-thymine temporary negative ion that is photodetached with a near-IR probe pulse. The resulting photoelectrons are analyzed with veloc...

The kinetics of thymine-thymine cyclobutane pyrimidine dimer (TT-CPD) formation was studied at 23 thymine-thymine base steps in two 247-base pair DNA sequences irradiated at 254 nm. Damage was assayed site-specifically and simultaneously on both the forward and reverse strands by detecting emission from distinguishable fluorescent labels at the 5'-termini of fragments cleaved at CPD sites by T4...

While investigating the effects of structural analogues of thymine on the thymine-requiring strain of E&cherichia coli 15 T we noticed the presence in the bacterial deoxyribonucleic acid of a new base which we have identified as 6-methylaminopurine. Although 6-methylaminopurine is usually present in small amounts (2% of the adenine) in the deoxyribonucleic acid of E. coli 15 Tits relative propo...

Laboratory experiments have shown that the UV photo-irradiation of low-temperature ices of astrophysical interest leads to the formation of organic molecules, including molecules important for biology such as amino acids, quinones, and amphiphiles. When pyrimidine is introduced into these ices, the products of irradiation include the nucleobases uracil, cytosine, and thymine, the informational ...

Thymine-requiring Escherichia coZi 15, tand E. coli B, twhich contained 5-bromouracil in their deoxyribonucleic acid in place of thymine showed a marked increase in sensitivity to ultraviolet (u.v.) radiation. The effect was proportional to the extent of incorporation of 5-bromouracil under defined growth conditions and for a given medium. This increase in sensitivity to U.V. was not hereditary...