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

Monkey kidney cells (CV-1) grown for 4 h in the presence of 0.1 m M 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.