I have the following function, which updates the User Initiated Send definition to a new Data Extension. I would like to know how to update the email name too.

function runUIS(UISKey,DEName){
            var deESD = Send.Definition.Init(UISKey);
            var updatestatus = deESD.Update({"DataExtensionKey":"SendDE","XXXX":"EmailName"});

I have tried various object names (for XXXX): Email | EmailKey | Message | MessageKey | EmailSendKey | EmailSend | ESD | EmailMessage and none of them seem to work.

The wiki page doesn't tell what this value is either: http://help.exacttarget.com/en/documentation/exacttarget/content/server_side_javascript/server_side_javascript_syntax_guide/send_server_side_javascript_functions/

Does anyone know what the object name might be, or how to find it?