Chord sequence
C♯7 F♯7 B7 E7 Amaj7
In every key
Four-note rootless voicings in their two forms, with the 3rd or the 7th on the bottom, played over the root.
Heard in A major
All the chords
Dominant 7th chords around the cycle of fifths, each the V of the next, from III7 to V7 and home to I.
Over C#7 · V7/VI
Mode 6 of Blues
Over F#7 · V7/II
Over B7 · V7/V
Mode 5 of Major
Over E7 · V7
Over Amaj7 · Imaj7
The major scale and its modes are the most commonly used scales in western music.