Study the following series.
5 2 G 6 U % F C 8 K B P V 3 L E R 4 9 M
Find what should come in place of the question mark(?)
U8 , ? , 8B , BP
There is a gap of 1 between the first characters of each of the given pair. The second character of each pair is decreasingly moving one position to the right of the first character.