Extraction of sequences and ribosome scanning model (RSM). The ribosome scans the mRNA sequence from 5’ to 3’ until it reads an ATG codon with an appropriate context. If the AUG codon has an appropriate context, the translation initiates at that site and terminates when a stop codon is read. An in-frame codon is represented by three consecutive nucleotides that are grouped together. Part (a) of the figure presents an example of extraction of positive sequences (TIS) and parts (b) and (c) present out of frame and in frame negative sequences, respectively.