Had a query on Roles and Permissions in WCM.

In WCM environment, I have an article which falls in a List (This list
has permissions for users from Groups à Authors, Approvers) . I have
assigned audience of these role type for this article.

When this article is published, it should be viewable only to the
Groups : Authors and Approvers. How do I assign such a rule ??

Any help would be highly appreciated.