Final answer:
Start codon AUG in vertebrates and vascular plants is more efficiently recognized for translation initiation when it is surrounded by the consensus sequence specified in Kozak's rules, which is '5'-gccRccAUGG-3', where 'R' indicates a purine base (adenine or guanine).
Step-by-step explanation:
For translation in vertebrates and vascular plants, the AUG used as the start codon requires specific bases in the surrounding sequences, which according to Kozak's rules, need to include a consensus sequence: 5'-gccRccAUGG-3'. Here, R represents a purine base, which can be either adenine (A) or guanine (G), but not cytosine (C) or uracil (U). The existence of this sequence around the AUG start codon ensures higher efficiency of translation initiation in eukaryotic organisms. Initiation factors (IFs) and the cap-binding protein (CBP) move the ribosome to the mRNA's 5' cap, then the initiation complex scans for the AUG start codon. When the sequence closely matches the Kozak consensus sequence, the correct initiation site is recognized more efficiently.