bookworm-trying to be clear, so sorry of i am not
As gravity acts vertically downwards the aircraft decends with the resulting airflow hitting (for want of a better word) the fin area, with the fuselage acting as a lever arm, which in turn yaws the nose into the turn.
There is coupled with this the loss of lift in a turn due to lift acting at 90 degrees to the relative airflow. Actually, to explain that better than i ever could here. If you have a flight training manual 1 (PPL air pilots), go to medium level turns and look at the forces in a turn section.