Abstract: Certain aspects of the invention provide nucleic acid constructs that can be used to cause a cell to be dependent on a particular enzymatic activity or on the presence of a particular small molecule. Certain aspects of the invention also provide methods for cloning genes involved in the synthesis, modification or degradation of a given molecule and for the directed evolution of proteins that perform a specified enzymatic function. Certain methods of the invention can be used to isolate the genes responsible for directing the biosynthesis, modification or degradation of a particular target molecule and to isolate polypeptide variants having new or improved enzymatic activity.

Abstract: The present invention relates to altering the physical and/or chemical properties of at least part of at least one tissue in the eye. In a specific embodiment, it relates to the treatment of any eye disorder, although in particular embodiments the individual has a thickened Bruch's membrane. An activating energy source is utilized to effect a controlled diffusion enhancement and/or degradation of Bruch's membrane that enables improved diffusional transport between the choroid and retina. The individual is administered an inactivated diffusion-enhancing molecule that becomes associated with the membrane, which is then precisely exposed to an activating energy source, such as light or ultrasound.

Abstract: Certain aspects of the invention provide nucleic acid constructs that can be used to cause a cell to be dependent on a particular enzymatic activity or on the presence of a particular small molecule. Certain aspects of the invention also provide methods for cloning genes involved in the synthesis, modification or degradation of a given molecule and for the directed evolution of proteins that perform a specified enzymatic function. Certain methods of the invention can be used to isolate the genes responsible for directing the biosynthesis, modification or degradation of a particular target molecule and to isolate polypeptide variants having new or improved enzymatic activity.