Improved system for capillary microinjection into living cells

The effect of inhibition of protein synthesis on the synthesis and processing of low molecular weight RNA (LMW RNA) hs been studied on CHO-tsH1, a mutant cell line in which protein synthesis is rapidly inhibited at non-permissive temperature by inactivation of the enzyme leucyl-tRNA synthetase. The increase in temperature results in an increase in uridine uptake and in the specific activity of UTP pool which is probably not related to the mutation. We report in this paper that there is no significant alteration in the synthesis of LMW RNA (including 5S ribosomal RNA (rRNA) and tRNA) except for the inhibition of synthesis of nucleolar RNA species A. Since, in a previous paper, it has been shown that the processing of preribosomal nucleolar RNA does not proceed at 39.5 degrees C in CHO-tsH1 cells, these results are consistent with the hypothesis that nucleolar RNA species A is involved in the processing of rRNA depends on its synthesis and maturation.