"I Am who I Am"
Out of respect for the holiness of God, the people of Israel do not pronounce his name. In the reading of Sacred Scripture, the revealed name (YHWH) is replaced by the divine title "LORD" (in Hebrew Adonai, in Greek Kyrios). It is under this title that the divinity of Jesus will be acclaimed: "Jesus is LORD."
Source: Catechism of the Catholic Church (Vatican.va)