Figure 2. The TIS sequence and eIFs mediate initiation of translation. (A) 43S preinitiation complex (40S, eIFs 1, 1A, 2, 3, 5, and initiator Met-tRNA) recognizes a TIS sequence (in this example, GCCACCAUGGC with start codon underlined). (B) eIF5B is loaded while others detach. This allows the joining of the 60S ribosomal subunit to form the 80S complex. After shedding the remaining eIFs, (C) protein elongation begins. Initiator Met-tRNA, red L; eIFs, white circles; bases represent the TIS sequence.