MEDLINE Indexing Online Training Course
If an article discusses basic biology of a gene/protein from certain organisms, indexers must also link the gene/protein to the appropriate record in the NCBI data base called Entrez Gene. The gene/protein must be the main focus of the article. The list of organisms for which gene links are made is growing constantly.
Detailed instructions for creating these links are given in Chapter 37 of the Indexing Manual (NLM staff access only).