Which letter-cluster will replace the question mark (?) to complete the given series?

GSAV, JPER, ?, PJMJ, SGQF

MMIN

Explanation:

GSAV, JPER, ?, PJMJ, SGQF

The logic followed here is :

G → (+3) → J → (+3) → M → (+3) → P → (+3) → S

S → (-3) → P → (-3) → M → (-3) → J → (-3) → G

A → (+4) → E → (+4) → I → (+4) → M → (+4) → Q

V → (-4) → R → (-4) → N → (-4) → J → (-4) → F

So, the letter-cluster that replaces the (?) to complete the series is "MMIN"