Definition a submitter-supplied, systematic, stable identifier for a gene and its associated features, used for tracking purposes
Value Format
"text"(single token) 
but not "<1-5 letters><5-9 digit integer>[.<integer>]"
Example /locus_tag="ABC_0022"
Comment /locus_tag can be used with any feature that /gene can be used with; identical /locus_tag values may be used within an entry/record, but only if the identical /locus_tag values are associated with the same gene; in all other circumstances the /locus_tag value must be unique within that entry/record. Multiple /locus_tag values are not allowed within one feature for entries created after 15-OCT-2004. If a /locus_tag needs to be re-assigned the /old_locus_tag qualifier should be used to store the old value. The /locus_tag value should not be in a format which resembles INSD accession numbers, accession.version, or /protein_id identifiers.