DataContractSerializer and objects with interface members

Hi,

I have a class with interface members (similar to the code below):

[DataContract]
public class MyClass : IMyClass
{
[DataMember]
protected IMySubClass[] myAvailableSubClasses;
[DataMember]
protected IMySubClass myCurrentlySelectedSubclass;

...
...
...
}

Now the DataContractSerializer is able to serialize the object but not
to deserialize it. I guess it doesn't know how to instantiate a
interface. Is there a work-around? I need to use the interfaces because
I have different implementations of the sub class objects.

Kind Regards

Fabian