Help with turret script.

I’ve been trying to get a turret working. The turret is 2d and simply has to shoot towards where the mouse is pointed.

Here is my code so far:

var prefabShot:Transform;

function Update () {
	var x1 = Input.mousePosition.x;
	var y1 = Input.mousePosition.y;
	var x2 = screenPos.position.x;
	var y2 = screenPos.position.y;
	var angle = Mathf.Atan2(y2 - y1,x2 - x1);
	
	transform.rotation = Quaternion.Euler(0,0,angle);
	if(Input.GetButtonDown("Shoot"))
	{
		Instantiate(prefabShot, transform.position + Vector3.right*2, Quaternion.Euler(0, 0, 90));
	}  
}

you can check this trade for an example
http://forum.unity3d.com/threads/98598-Trajectory-calculations!

thanks that link helped a lot.