Screen Mode
          
      G, A, T, . . .   - insert a sequence character
      <Delete>         - delete a sequence character
      <Ctrl>H          - delete a sequence character
      /TAACG<Return>   - find the next occurrence of TAACG
                           (last pattern entered is the default)
      1<Return>        - move to start of the sequence
      <Ctrl>E          - move to end of the sequence
      [n]<Right-arrow> - go ahead n characters
      [n]<Left-arrow>  - go back  n characters
      <Up-arrow>       - go up to check sequence
      <Down-arrow>     - go down to original sequence
      'markcharacter   - go to marked position
      37<Return>       - go to position 37 (any positive integer)
      <                - go back  50 characters
      >                - go ahead 50 characters
      <Ctrl>R          - redraw the screen
      <Ctrl>D          - enter command mode
[n] is an optional numeric parameter.