Hook started the tournament by playing full-back in the opening defeat to England before switching to No.10 for the morale-boosting triumph over Scotland at Murrayfield.
Davies has failed to recover from a hamstring injury and in the absence of Gavin Henson, Tom Shanklin and Andrew Bishop, Hook was the only option to move into the midfield.
"We have selected the strongest possible side, showing the utmost respect to Italy," said head coach Gatland.
"We know only too well what tough opponents they are in Rome and so we have picked the strongest team available to us."
Aside from the absence of Davies and the return of Jones, Gatland has kept faith with the side that defeated Scotland 24-6 for their first win in nine tests.
Leigh Halfpenny returns to the replacements bench after recovering from a hamstring injury and should feature as Wales look to improve on their 20-15 victory in 2009.
15 - Lee Byrne (Ospreys)
14 - Morgan Stoddart (Scarlets)
13 - James Hook (Ospreys)
12 - Jamie Roberts (Cardiff Blues)
11 - Shane Williams (Ospreys)
10 - Stephen Jones (Scarlets)
9 - Mike Phillips (Ospreys)
1 - Paul James (Ospreys)
2 - Matthew Rees (Scarlets) (captain)
3 - Craig Mitchell (Ospreys)
4 - Bradley Davies (Cardiff Blues)
5 - Alun-Wyn Jones (Ospreys)
6 - Dan Lydiate (Newport Gwent Dragons)
7 - Sam Warburton (Cardiff Blues)
8 - Ryan Jones (Ospreys)
16 - Richard Hibbard (Ospreys)
17 - John Yapp (Cardiff Blues)
18 - Jonathan Thomas (Ospreys)
19 - Josh Turnbull (Scarlets)
20 - Tavis Knoyle (Scarlets)
21 - Rhys Priestland (Scarlets)
22 - Leigh Halfpenny (Cardiff Blues)