I Walk the Line - chords, tab and comments

This incredible simple song was released 1956 by Hi-Lo Music, and recorded at Sun Studio, Memphis. They wondered what the heck that guy was doing ... but before anyone answered he'd already done that. The "boom-chicka-boom" rhythm and Johnny's young, but still dark voice made it to the top of the charts, despice it's simplicity - or maybe because of.
This hit was never covered by anyone successfully. I play it sometimes: when my hatch is drained with strong coffee and maybe some booze, I may hit the lowest B note. Maybe not. Johnny himself did not at San Quentin, and producer Bob Johnston drowned the goof in wild applause.
A brief note upon the "boom-chicka-boom" style I've put HERE.
E       B7                          E
I keep a close watch on this heart of mine
           B7                     E
I keep my eyes wide open all the time
            A                          E 
I keep the ends out for the tie that binds
                B7               E
because you're mine I walk the line 

The "Tennessee Two" or "Three": including W.S. Holland on drums in addition to Luther Perkins and Marshall Grant, tuned their instruments sharp, performing "F" instead of "E" on stage and in studio.
The stunt with the song is swapping keys, starting E major, down to A major, up to D major, down to A major, rounding up with 1st verse down E major low. I won't list it all up here, only the first one - E major - simplicity rules :-)
E major
B 7th
A major
Johnny Cash