As announced previously, we have introduced cross-product definitions, in the form of intersection_of tags, into the "extended" version of GO (ontology/obo_format_1_2/gene_ontology_ext.obo).

The first cross-products in GO were added on January 18, 2010, and provide computable definitions for regulation terms in the biological process ontology. More "internal" cross-products, i.e., those that reference only terms within the GO, will be added in the coming weeks.

For more information, please see the cross-product documentation and intersection tag documentation, or write to the GO helpdesk.