Does the government have an obligation to grant use immunity to witnesses that have been designated as potentially helpful to the defense?

The government is under no general obligation to grant use immunity to witnesses the defense designates as potentially helpful to its cause but who will invoke the Fifth Amendment if not immunized. United States v. Turkish, 623 F.2d 769, 774 (2d Cir.1980) (discussing difference between prosecutorial powers and obligations and those of a defendant). See also United States v. Praetorius, 622 F.2d 1054, 1064 (2d Cir.1979) (refusing to require the government to confer use immunity absent "extraordinary circumstances").