FACTBOX: Candidates for Pakistan's September 6 presidential vote

(Reuters) - Pakistan holds a presidential election on Saturday to replace Pervez Musharraf, who resigned on August 18 under threat of impeachment by the coalition government led by the party of assassinated former prime minister Benazir Bhutto.

Under Pakistan's constitution members of the country's four provincial assemblies and the two-chamber national parliament elect the president.

Here are some facts about the three presidential candidates:

ASIF ALI ZARDARI

* Former prime minister Benazir Bhutto's widower and political successor, Zardari was thrust into the centre of politics by his wife's assassination on December 27, and then to the centre of power after their Pakistan People's Party (PPP) won the most seats in a February 18 election.

* Born in the southern province of Sindh to a land-owning family, the telegenic Zardari, 53, has long been controversial.

* He served as a minister in his wife's second government in the 1990s, and was a senator until 1999, but was accused of getting kickbacks on government deals and earned the nickname "Mr 10 Percent".

* Zardari spent in all 11 years in prison on charges of corruption and murder, although he denied all accusations and was never convicted. He was released on bail in 2004.

* Last year, Musharraf granted an amnesty to Bhutto, Zardari and other PPP leaders from graft charges under a power-sharing deal with Bhutto.

* The PPP has rejected a report Zardari was mentally unstable, saying he was tortured in prison and as a result had been under mental stress and had had a heart problem, but was never mentally ill.

* He married Bhutto in 1987 and they had three children -- two girls and a boy.

* Analysts say Zardari should have enough electoral college votes to win.

SAEEDUZZAMAN SIDDIQUI

* Siddiqui is a former judge, nominated for the post of president by former Prime Minister Nawaz Sharif's party, the Pakistan Muslim League (Nawaz), which came second to the PPP in February parliamentary elections.

* The soft-spoken Siddiqui was a Supreme Court judge when he ruled in favour of then Prime Minister Sharif in a confrontation with the judiciary in 1997.

* Siddiqui lost his job as a Supreme Court judge after then army chief Musharraf overthrew Sharif in a 1999 coup and demanded an oath of allegiance from members of the judiciary.

* Born in 1937 in Calcutta, in what was then British-ruled India, Siddiqui moved to Pakistan with his family in 1956.

MUSHAHID HUSSAIN SAYED

* Sayed was nominated by the Pakistan Muslim League which backed Musharraf and ruled under him. After the February elections it was the main opposition party in parliament until Sharif's PML (N) broke away from the ruling coalition last week.

* Sayed, a former journalist, served as information minister in Sharif's cabinet until the government was forced from power by Musharraf's 1999 coup.

* He was detained for more than a year after the coup but upon his release joined the party Musharraf cobbled together to provide him with a base of support, and was elected as a senator.

* He later became secretary general of the so-called King's Party, a moderate face in a conservative party that was defeated in a February 18 general election.

* The son of an army colonel, the astute, affable Sayed studied at Georgetown University in Washington.

(Reporting by Kamran Haider; Writing by Jerry Norton; Editing by Robert Birsel)