---
layout: rule
id: GORULE:0000051
title: "Some GO terms require a value in the Annotation Extension field"
type: report
fail_mode: soft
status: proposed
contact: "go-quality@lists.stanford.edu"
implementations:
---
Direct annotations to these terms require a value in the Annotation Extension field: 

 * 'GO:0005515 protein binding' 
 * 'GO:0005488 binding'

For more information, see the [binding guidelines](http://wiki.geneontology.org/index.php/Binding_Guidelines)
on the GO wiki.

This rule may be expanded in the future to include other terms such as 'GO:0008283 cell population proliferation'.