4‐THIOURIDINE INCORPORATION INTO THE RNA OF MONKEY KIDNEY CELLS (CV‐1) TRIGGERS NEAR‐UV LIGHT LONG‐TERM INHIBITION OF DNA, RNA AND PROTEIN SYNTHESIS

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Abstract
Monkey kidney cells (CV‐1) grown for 4 h in the presence of 0.1 mM 4‐thiouridine (s4Urd) incorporate this photoactivable uridine analog in their RNA. A minor, 5–8%, thiolated RNA fraction can be isolated from bulk RNA by affinity chromatography. This RNA fraction contains 1.5–2.5 s4Urd residues per 100 nucleotides and exhibits a broad chain length distribution ranging from 700 to 7000 nucleotides. It is essentially of nuclear origin and amounts to 30% of the RNA synthesized during exposure of cells to s4Urd. Under the same s4Urd labeling conditions, no thiolated pyrimidine residues have been detected in DNA.Irradiation with 365 nm light (45 kJ/m2) of the cells immediately after s4Urd exposure triggers long‐term inhibition of DNA, RNA and protein synthesis accompanied by a linear decline (50% in 2 days) in the total cell mass of cultured cells. In contrast, exposure to s4Urd alone results in moderate but reversible inhibitory effects. The available data suggest that s4Urd‐induced photolesions in newly synthesized RNA such as RNA‐RNA cross‐links as well as RNA‐protein bridges are directly involved in impairment of essential cellular functions.