Drop down does not postback within ajax update panel

Was hoping to avoid a whole page refresh by wrapping couple of controls (drop down and text box) inside script manager but postback doesn't work. 

<asp:UpdatePanel ID="UpdatePanel1" runat="server"><ContentTemplate><p><label for="location">
                            Location - Which part of the UK do you reside?</label><br /><asp:DropDownList ID="ddlLocation" runat="server" AutoPostBack="true"><asp:ListItem>test1</asp:ListItem><asp:ListItem>test2</asp:ListItem><asp:ListItem>Other</asp:ListItem></asp:DropDownList></p><asp:Panel ID="pnlLocationOther" runat="server" Visible="false"><p><label for="locationother">
                                Other Location (Please specify)</label><br /><input type="text" name="locationother" required="required" id="locationother" maxlength="100"
                                value='<%= Request.Form["locationother"] %>' /></p></asp:Panel></ContentTemplate></asp:UpdatePanel>