FACTBOX-Turkish presidential election procedure

ANKARA (Reuters) - Turkey's Islamist-rooted ruling AK Party plans to propose its presidential candidate to parliament again after the Constitutional Court ruled invalid the first round of the election.

Here are some facts about the process:

* Parliament chooses the president in a series of up to four votes. In the first and second rounds, a candidate must receive 367 votes, or two-thirds of all deputies. In the third round, a candidate needs only a simple majority -- 276 votes. If a fourth round produces no winner, a parliamentary election is called.

* The Constitutional Court has cancelled last week's first round vote, ruling that not enough members of parliament were present. The court upheld an appeal from the main opposition party, which boycotted the vote, that a quorum of 367 deputies was needed.

* The government will repeat the first round, attempting to secure a quorum. It can repeat the first round again, but must complete all rounds within 30 days of the start of the nomination process. This began on April 16, meaning that the new president is due to be sworn in on May 16. A three-day interval is needed between each round, making the timetable very tight now. A new schedule will be set out on Wednesday.

* Foreign Minister Abdullah Gul, a former Islamist and a member of the last government to be pushed from office by the army, remains the only candidate for president as the period for nominations has closed.

* The government has said it is prepared to call an early election on condition that the minimum age for members of parliament be 25 years. Parliament has already passed a law to reduce the minimum age from 30, but a constitutional amendment still has to be made. The AK Party said on Tuesday it had presented the draft amendment to parliament, according to the state news agency Anatolian.