Independent Pursuits: Puzzle

WHAT IS the next letter in this series: X, J, U, O, M, J, U... ?

and this one:

T, B, O, N, T, B, T, I, T...?

(answers tomorrow).

Answer to yesterday's puzzle:

MEANT LOWER is the odd one out: a watermelon is not an animal, unlike kangaroo, elephant, rhinoceros and giraffe.