Which letter will replace the question mark (?) in the following series? S31T, U37V, W41X, ?

X43Y Y47Z Y43Z A43B

Y43Z

According to the above alphabet position: S31T    ⇒ (19), 31, (20) U37V   ⇒ (21), 37, (22) W41X  ⇒ (23), 41, (24) ?         ⇒ (25), 43, (26) = Y43Z (consecutive alphabet series at 1st and last alphabet position and there is prime number series in the middle)