Role of silicon in diatom metabolism. Messenger RNA and polypeptide accumulation patterns in synchronized cultures of Cylindrotheca fusiformis.

Patterns of in vitro translation products from isolated mRNA and in vivo polypeptide accumulation in synchronized cultures of Cylindrotheca fusiformis were analysed by two-dimensional gel electrophoresis. The way in which the availability of silicon, the specific cell cycle stage, or the illumination conditions affected the pattern of gene expression was distinguished by comparing the timing of polypeptide and mRNA accumulation in cultures synchronized by two different methods. A rapid and dramatic shift in the relative abundance of in vitro translation products from mRNA followed either the removal or the readdition of silicate to the media as well as the transition from dark to light. Eleven mRNAs appeared to be expressed specifically between mid-S phase and cell separation, as their increase was observed at this stage in both synchronies. In addition, three mildly acidic polypeptides from the soluble protein fraction of C. fusiformis, each representing about 0.05% of the total protein, increased several-fold between mid-S and cell separation. Thus, silicon appears to affect gene expression both directly and, due to its effect on cell cycle progression, indirectly. Both effects are primarily at a level before translation.