  Many proteins interact with and deform double-stranded DNA in cells.
Single-molecule experiments have studied the elasticity of DNA with
helix-deforming proteins, including proteins that bend DNA. These experiments
increase the need for theories of DNA elasticity which include helix-deforming
proteins. Previous theoretical work on bent DNA has examined a long DNA
molecule with many nonspecifically binding proteins. However, recent
experiments used relatively short DNA molecules with a single, well-defined
bend site. Here we develop a simple theoretical description of the effect of a
single bend. We then include the description of the bend in the finite worm
like chain model (FWLC) of short DNA molecules attached to beads. We predict
how the DNA force-extension relation changes due to formation of a single
permanent kink, at all values of the applied stretching force. Our predictions
show that high-resolution single-molecule experiments could determine the bend
angle induced upon protein binding.
