AK in SB, $100NL

[CourtesyFlush]

What's my play here? UTG was a fairly tight solid player, not sure about MP.

Party Poker No-Limit Hold'em, $ Hero (6 max, 6 handed) pokerhand.org hand converter

UTG ($202.28)
MP ($105.09)
CO ($105.90)
Button ($138.68)
SB ($100.55)
Hero ($151.10)

Preflop: Hero is BB with K[img]/images/graemlins/diamond.gif[/img], A[img]/images/graemlins/diamond.gif[/img]. SB posts a blind of $0.50.
<font color="#CC3333">UTG raises to $4</font>, MP calls $4, <font color="#666666">3 folds</font>, Hero calls $3.

Flop: ($12.50) K[img]/images/graemlins/spade.gif[/img], A[img]/images/graemlins/spade.gif[/img], J[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(3 players)</font>

Hero ?

What is my move and why?