Read File Name from Keyboard and Open This File

.MODEL SMALL
        .DATA

                MSG  DB  0DH,0AH, ' ENTER THE FILE NAME :-----> :  $'
                STR1 DB  255 DUP('$')
                Buffer DB 10 dup(0)
                Handle dw ?
               ; ONE  DB ?
          .CODE

BEGIN:
          MOV AX,@DATA
          MOV DS,AX

          LEA DX,MSG
          MOV AH,09H
          INT 21H

          LEA SI,STR1
          MOV AH,01H

READ:
          INT 21H
          MOV [SI],AL
          INC SI
          CMP AL,0DH
          JNE READ

DISPLAY:
          LEA DX,STR1
          MOV AH,09H
          INT 21H
OPENFILE:
                mov     ah, 3dh         ;Open the file
                mov     al, 0           ;Open for reading
                mov     dx, STR1        ;Presume DS points at filename
                int     21h
                jc cant_open
                mov handle, ax              ; segment.

READFILE:
                mov     ah,3fh              ;Read data from the file
                mov     bx, handle
                lea     dx, offset Buffer      ;Address of data buffer
                mov     cx, 10         ;Get file handle value
                int     21h

EOF:
                mov bx, handle
                mov     ah, 3eh         ;Close file
                int     21h

cant_open:

 MOV AX, 4C00H
 INT 21H


        .EXIT
END BEGIN


I am getting A2070 error on "mov     dx, STR1        ;Presume DS points at filename" line. Could you help me?