10 Dec, 12:23
Ireland's John Lacey will referee his first ever RBS 6 Nations match in February, while Alain Rolland is also included in the Elite Panel in what is his last season.
Any slip-up by the top two could let the winners of what will undoubtedly be the game of the round - the interprovincial derby between Munster and Leinster at Thomond Park on Saturday - take over at the summit.
The remaining two games on Friday night see both Italian sides in action, Benetton Treviso hosting Connacht at Stadio Monigo and Zebre making their second visit to Wales this season - this time to play the Newport Gwent Dragons.
Zebre currently sit in 10th place in the table, behind Treviso purely on points difference - just three points, or the value of a penalty kick, separates the two teams.
Having tasted victory over the Cardiff Blues on their last trip to Wales, Zebre will be anxious to repeat the feat, while Treviso are building up a reputation as a difficult team to beat at home.
The round wraps up on Sunday with the clash of the capital cities - Cardiff facing Edinburgh at the Arms Park. Neither team has made the start to the season they had perhaps hoped for, and a victory for either side going into the break would be a welcome bonus.
RABODIRECT PRO12 - ROUND 5 FIXTURES:
Friday, October 4 -
Ospreys (2nd) v ULSTER (5th), Liberty Stadium, 7.05pm (live BBC 2 Northern Ireland/BBC 2 Wales)
Benetton Treviso (9th) v CONNACHT (11th), Stadio di Monigo, 8.30pm local time/7.30pm Irish time (live TG4/Mediaset)
Newport Gwent Dragons (7th) v Zebre (10th), Rodney Parade, 7.15pm
Saturday, October 5 -
MUNSTER (3rd) v LEINSTER (4th), Thomond Park, 6.45pm (live RTÉ Two)
Scarlets (6th) v Glasgow Warriors (1st), Parc y Scarlets, 6.30pm (live S4C/BBC ALBA)
Sunday, October 6 -
Cardiff Blues (8th) v Edinburgh (12th), Cardiff Arms Park, 2.05pm (live BBC 2 Wales/BBC ALBA)