The effect of 5-fluoroorotic acid on the early labelling of nucleotides and RNA in whole liver and of RNA in subnuclear fractions in rats given 3H-orotic acid.

Abstract

Male white rats were given either orotic acid or 5-fluoroorotic acid 60 min, and 3H-orotic acid 3 1/2 min before sacrifice. Liver nucleotides were analyzed by isotachophoresis. The (F)UTP pool increased to the same extent in both groups and showed the same specific labelling. The RNA synthesis, as measured by nmol of UTP entering RNA-UMP/g wet liver tissue was significantly lower in fluoroorotic acid treated rats. In the nucleolar fraction there was an increase in the RNA/DNA ratio, a decrease in the specific RNA labelling and an essentially unaltered specific labelling of RNA/microgram/DNA. The effect on the specific labelling of RNA/microgram DNA was the same in the nucleolar fraction and the nucleolar-free pellet, suggesting that the transcription of RNA in these two fractions proceeded in a similar way. There was a slight increase in the specific RNA labelling of the supernatant subnuclear fraction, containing low-molecular weight RNA. Incorporation into UDP-hexoses and UDP-N-acetylhexosamine was unchanged.