The agreement that eased Yemeni President Ali Abdullah Saleh out of office after three decades in power and following a year of protests calls for the national dialogue to produce a new constitution and electoral law.
But the "Southern Movement participation in the national dialogue is a 'make or break' issue," said April Longley Alley, a senior analyst from the International Crisis Group.
"A critical mass of participants from the movement is an essential element for reaching a valid compromise on the structure of the state," Alley wrote in a report coinciding with the anniversary.
The national dialogue conference, originally scheduled to take place in mid-November, has been delayed after factions in the Southern Movement, which has campaigned for autonomy or outright secession for the formerly independent south, refused to join the talks.
UN Secretary General Ban Ki-moon on a visit to Yemen this week pointed to southern grievances that have fanned separatist sentiment, citing demands for "compensation for land and property (and) jobs lost after unification" in 1990.
And his special envoy to Yemen, Jamal Benomar, on Friday urged "all political leaders and the preparatory committee of the national dialogue to address the pending issues."
"The transition in Yemen remains fragile, and the stakes are high. It's still threatened by those who have not embraced change in the country," he warned.
Planning Minister Mohammed al-Saadi, speaking to AFP, has acknowledged that "the southern issue is a priority on the agenda of the national dialogue and the key to the future" of Yemen.
The dialogue's preparatory committee has proposed a series of measures to President Abdrabuh Mansur Hadi to restore the southerners' confidence in the Sanaa government.
These measures include reinstating or compensating some 60,000 civil servants, military and police officials "unfairly" fired or sent into early retirement during Saleh's rule, according to a member of the committee.
But "with separatist sentiment strong and virtually no action from the central government to demonstrate a new political era, it is difficult" for the Southern Movement leaders to participate, says Alley.
After North and South Yemen unified in 1990, the south broke away in 1994. The move sparked a short-lived civil war that ended with the region being overrun by northern troops.
In 2007, the Southern Movement emerged as a social protest movement of retired officials and soldiers. But it has gradually grown more radical in its demands.
-- 'Good step' --
Yemenis must hold the national dialogue based on the Gulf and UN-brokered power transfer deal in which Hadi replaced Saleh.
The talks are intended to result in a new constitution and prepare for legislative and presidential elections at the end of Hadi's two-year interim period in February 2014.
Saadi said he expected differences to be ironed out this month and that the dialogue would begin "in December."
The preparatory committee announced on Wednesday that 50 percent of the national dialogue seats have been allocated to southerners, according to state news agency Saba, in a step clearly aimed at convincing the separatists to join the talks.
"This is a good step," southern activist Qasem Dawoud told AFP.
But the talks face other thorny issues.
Zaidi Shiite rebels, who have mounted repeated uprisings in the far north since 2004, and Sunni Salafists affiliated with the influential Islah (reform) Party are locked in frequent battles in the northern parts of the country.
Both groups are taking part in the dialogue.
Meanwhile, youth groups -- the main engines behind last year's uprising that ousted Saleh -- could stir controversy over the immunity offered to the former president in return for stepping down.
These groups, whose ranks saw hundreds of deaths during clashes with Saleh's troops, have repeatedly voiced their rejection of Saleh's immunity, granted under the deal signed on November 23, 2011.