That "is" defines "ought," or "The fact that a living entity is, determines what it ought to do," is clearly circular. Rand confuses this situation with her theory of moral choice which leaves the "ought" to choice and not to "is." This is the problem of pre-moral choice which has stymied Objectivist ethics for decades now.
If an ought is defined by an is, then how is this up to pre-moral choice? How can any choices be pre-moral? "Choosing life as your standard of value is a pre-moral choice. It cannot be judged as right or wrong; but once chosen, it is the role of morality to help man to live the best life possible." http://importanceofphilosophy.com/Ethics_LifeAsMoralStandard.html
So it appears that Objectivism has not bridged the is-ought gap as long as there is at least one a-moral choice ("it cannot be judged as right or wrong"), the so-called "pre-moral choice."
"You have no choice about the necessity to integrate your observations, your experiences, your knowledge into abstract ideas, i.e., into principles." OPAR, 1. However true that may be, Objectivism has not bridged the gap enabling them to integrate facts of reality into moral prescriptions. We may have no choice than to integrate them, but the "how" of this is left up in the air. Objectivism therefore leaves man with no philosophical guidance to make the correct pre-moral choice, only highly romantic novels to convince his mind through escapist literature.