Initiator tRNA and Its Role in Initiation of Protein Synthesis

The initiation step of protein synthesis is quite differentfrom the repetitive steps of elongation that follow it. Initiation involves the assembly of the two ribosomal subunits, mRNA, and the initiator tRNA in a reaction requiring the participation of several initiation factors, and isoften the rate-limiting step in protein synthesis (Kozak1983; Gualerzi and Pon 1990; RajBhandary and Chow1995; Hershey and Merrick 2000). The initiator tRNAplays an important role in this process and in the selectionof the appropriate initiation codon. Because of its specialfunction, an initiator tRNA possesses many highly specific properties that are different from those of elongatortRNAs (RajBhandary 1994). We have been interested inidentifying the sequence and/or structural features in theinitiator tRNA important for specifying its distinctiveproperties and in understanding the molecular basis of thespecific interactions of the initiator tRNA with the various proteins, the initiation factors, and the ribosome.Here we report on our work with the eubacterial Escherichia coli initiator tRNA. We describe briefly the systemthat we use for in vitro and in vivo functional analyses ofmutant initiator tRNAs, a summary of the overall results,and some of our conclusions related to participation ofthe tRNA in initiation...