A rare-codon-based translational program of cell proliferation

The codon usage of mRNAs controls the speed of translation elongation, which is primarily determined by the abundance of cognate tRNAs. By profiling mRNA expression around the cell cycle we found that mRNAs that are relatively upregulate in the G2/M phase are enriched in rare codons. To understand the impact of this codon bias on translation, we have cultured NIH 3T3 cells with different concentrations of fetal calf serum (FCS), 1, 2, 5, and 10%, respectively, to induce distinct proliferation rates and thus distinct proportions of cells in the culture in the G2/M phase. We then estimated the levels of all proteins and mRNAs, and the change in translation efficiency (proteins per mRNA) in highly (10% FCS) relatively to less highly proliferating cells (lower FCS concentrations).