Primer as Sealer?

[Mr Real Nice]

Is it necessary to seal even for an opaque finish?  Seems like after the grain is filled, I should be able to go right onto the primer, no?  I'm using poly paint with SprayMax 2k Rapid Primer Filler as the primer coat.  Would the primer act as a sealer, too?

 

[Liam]

The stuff I used on my j-bass refinish (B-I-N shellac-based primer) claims that it works great as a sealer.