Effect of nutrient deprivation on ribosomal RNA and ribosomal protein mRNAin cultured mosquito cells

The effect of nutrient deprivation on RNA and protein synthesis in cultured Aedes albopictus mosquito cells was investigated by replacing the culture medium with phosphate-buffered saline. After a 2 h starvation treatment, in corporation of radio-labeled precursor into total RNA was inhibited by 50%, and after 4 h, incorporation of amino acids into protein was inhibited by 50%. To investigate directly the effects of starvation on rRNA synthesis, r ibosomal subunits were prepared from treated cells by sucrose density gradi ent centrifugation. After 4 h in saline, incorporation of [H-3]uridine into ribosomal subunits had declined to baseline levels. Even after 8 h starvat ion, however, the effect was reversed by refeeding with complete medium, in which cells resumed rRNA synthesis and ribosomal subunit assembly. During 8 h starvation, total amounts of rRNA detected by northern blot remained st able. Ribosomal protein mRNA abundance was measured on northern blots, usin g probes corresponding to L8 and L31 ribosomal protein genes. The content o f these ribosomal protein mRNAs was unchanged during starvation, or during treatment with actinomycin D. These results suggest that ribosomal protein mRNAs belong to a long-lived mRNA population, and suggest that post-transcr iptional regulation of ribosomal protein synthesis is an important regulato ry mechanism in growing mosquito cells. (C) 1998 Wiley-Liss, Inc.