The effect of formycin on the processing of transfer RNA precursors in the posterior silk gland of Bombyx mori.

Formycin, an adenosine analog, was used in studies of RNA synthesis by silk glands of silkworms in organ culture. Formycin has been shown to inhibit preferentially the incorporation of [3H]uridine into low molecular weight RNA in the cytoplasm. When silk glands were pulse-chase labeled with [3H]uridine in the presence of formycin, the synthesis of 4.5S tRNA precursors was not affected, as determined by gel electrophoresis. However, the accumulation of mature 4S tRNA was greatly reduced in the formycin-treated system, although the precursors synthesized disappeared from the 4.5S region on chase at the same rate as in the control system. [14C]Formycin was incorporated into the 4.5S precursors but not into 4S tRNA. These findings suggest that the inhibition of tRNA synthesis by formycin is due to the existence of some degradation mechanisms of formycin-containing 4.5S precursor RNA's and the failure to process them into normal 4S tRNA.