Control not at initiation? Bah, humbug!



Initiation is often assumed to be rate-limiting for protein synthesis, but the presence of rare codons nonetheless can influence protein levels. In this issue of The EMBO Journal, Chu et al report that when rare codons are positioned near the start of the coding region, ‘liberation’ of the initiation codon for loading of the next 40S subunit may be rate-limiting for initiation and therefore overall protein synthesis. The sequential nature of translation results in an interdependence in ribosome association either by de novo initiation or recycling. Thus, a more general view emerges where both elongation and initiation can contribute to protein expression.