Biological organisms must compactly store and yet efficiently read the
huge
amounts of genetic information contained in their DNA. Many DNA-based
enzymes involved in these processes function as highly processive molecular
motors capable of translocating over thousands of base pairs without
detaching from the DNA template. These motors face mechanical
obstacles to
their movement, especially in the highly packed DNA of chromatin, and
many
of these obstacles are known to be important regulators of gene
expression. I will discuss our recent progress towards
understanding the
stability of nucleosomes and the mechanism of transcription using
single-molecule, optical trapping approaches which complement ongoing
biochemical and structural studies.