The abundance of cytosolic mRNA does not necessarily correspond to the quantity of polypeptide synthesized in plant cells. The initiation of mRNA translation is regulated at the global and message-specific levels. mRNAs compete for discriminatory initiation factors that couple the 5'-(7m)GpppN-cap and the 3'-poly(A) tail of the RNA message. The resultant circularization of the mRNA promotes the association of the 43S pre-initiation complex that scans the 5'-leader for the initiation codon of the protein coding sequence. The physiological and developmental regulation of these events governs the level of polypeptide synthesis from endogenous and viral transcripts.