GO is a knowledge network

What Company Is Offering:
The GO provides a controlled vocabulary to describe gene and gene products in different organisms. GO is a knowledge network containing about 20.000 biological terms. It is built up as a directed acyclic graph starting from three basic areas namely:
the molecular function of gene products,
their role in multi-step biological processes, and
their localization to cellular components.

How It Works:

Knowledge-based search helps you to find the answers to your question faster. By using a domain ontology as structured background knowledge the search results are sorted into meaningful categories. You can use these categories to narrow your set of found articles to the relevant ones. In many cases the categories will already represent the answer to your question.

Type "rab5" and wait for the tree on the left to appear. Have a look at the "Top categories What, Who, Where and When". A click on biological process shows endocytosis and clicking on cellular component shows endosome as answers for this question.
More at:http://www.gopubmed.org/