NL25: Nut straight on flush board facing overbet

[Emperor Norton]

PokerStars No-Limit Hold'em, $0.25 BB (5 handed) Hand History Converter Tool from FlopTurnRiver.com (Format: 2+2 Forums)

Hero ($25.60)
Button ($24.55)
SB ($38.10)
BB ($44.10)
UTG ($36.80)

Preflop: Hero is MP with K[img]/images/graemlins/club.gif[/img], Q[img]/images/graemlins/diamond.gif[/img].
UTG calls $0.25, <font color="#CC3333">Hero raises to $1.25</font>, <font color="#666666">1 fold</font>, SB calls $1.15, <font color="#666666">1 fold</font>, UTG calls $1.

Flop: ($4) 6[img]/images/graemlins/spade.gif[/img], 9[img]/images/graemlins/club.gif[/img], J[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(3 players)</font>
SB checks, UTG checks, Hero checks.

Turn: ($4) T[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(3 players)</font>
SB checks, <font color="#CC3333">UTG bets $0.5</font>, <font color="#CC3333">Hero raises to $4</font>, SB folds, UTG calls $3.50.

River: ($12) 5[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(2 players)</font>
<font color="#CC3333">UTG bets $31.55 (All-In)</font>, Hero?

I should have c-bet the flop, but the SB rarely folds to c-bets, so I thought I might be better off drawing for free. What do you make of this river bet?