How to rotate an object without transform.Rotate

I have made a character that can rotate around its axis. The question is: how can I make it rotate around its axis without altering the two scripts, and giving the velocity of RotateSpeed of TP_Motor It uses two scripts. The first script is called character controller. By the way i have simplified the code with only the most important parts. This is the script code:

using UnityEngine; using System.Collections;

public class TP_Controller : MonoBehaviour {

 public static CharacterController CharacterController;
 public static TP_Controller Instance;

   void Awake() 
 {
     CharacterController = GetComponent("CharacterController") as CharacterController;
     Instance = this;
 }
   void Update() 
 {
     GetLocomotionInput();

     TP_Motor.Instance.UpdateMotor();
 }

 void GetLocomotionInput()
 {
     var deadZone = 0.1f;

     TP_Motor.Instance.VerticalVelocity = TP_Motor.Instance.MoveVector.y;

     TP_Motor.Instance.MoveVector = Vector3.zero;

    **// This is the part that should be altered//**

     if (((Input.GetAxis("Horizontal") > deadZone) && !Input.GetKey(KeyCode.LeftShift)) ||
         (Input.GetAxis("Horizontal") < -deadZone) && !Input.GetKey(KeyCode.LeftShift))
        transform.Rotate (0, Input.GetAxis("Horizontal"), 0); **// <-- SPECIALLY THIS!! //**

    TP_Animator.Instance.DetermineCurrentMoveDirection();

  }

  }

The second script is the TP_Motor. Here is the script:

   using UnityEngine;
   using System.Collections;

   public class TP_Motor : MonoBehaviour {

   public static TP_Motor Instance;

   public float RotateSpeed = 2.0F;

   public Vector3 MoveVector { get; set; }

   void Awake () 
 {
     Instance = this;
 }
 

 public void UpdateMotor () // Le cambie era UpdateMotor
 {
     ProcessMotion();
 }

 void ProcessMotion()
 {

 // First Movevector

     // Transform MoveVector to worldspace
     MoveVector = transform.TransformDirection(MoveVector);

     // Normalize MoveVector if Magnitude > 1
     if (MoveVector.magnitude > 1)
         MoveVector = Vector3.Normalize(MoveVector);

     // Multiply MoveVector by MoveSpeed
     MoveVector *= MoveSpeed();

     // Reapply VerticalVelocity MoveVector.y
     MoveVector = new Vector3(MoveVector.x, VerticalVelocity, MoveVector.z);

     // Apply Gravity
     ApplyGravity();

     // Move the character into world space
     TP_Controller.CharacterController.Move(MoveVector * Time.deltaTime);
 }

     public float MoveSpeed()
 {
     var MoveSpeed = 0f;

     switch (TP_Animator.Instance.MoveDirection)
     {

     // Turning

         case TP_Animator.Direction.TurningRight:
             MoveSpeed = RotateSpeed;
             break;
         case TP_Animator.Direction.TurningLeft:
             MoveSpeed = RotateSpeed;
             break;

         return MoveSpeed;
         }

        }

P.D. By the way i dont like transform.Rotate because it can make the character fall through the ground.