Complex sentence: However, few programs can handle all the "special" cases, such as the use of the alternative initiation codons; e.g., the rare alternative start codon CTG codes for Methionine when used as a start codon, and for Leucine in all other positions.
Split into simpler sentences: However, few programs can handle all the "special" cases, such as the use of the alternative initiation codons. For example, the rare alternative start codon CTG codes for Methionine when used as a start codon, and for Leucine in all other positions.