ROTARY DNA MOTORS

Many molecular motors move unidirectionally along a DNA strand powered by nucleotide hydrolysis. These motors are multimeric ATPases with mo re than one hydrolysis site. We present here a model for how these mot ors generate the requisite force to process along their DNA track. Thi s novel mechanism for force generation is based on a fluctuating elect rostatic field driven by nucleotide hydrolysis. We apply the principle to explain the motion of certain DNA helicases and the portal protein , the motor that bacteriophages use to pump the genome into their caps ids. The motor can reverse its direction without reversing the polarit y of its electrostatic field, that is, without major structural modifi cations of the protein. We also show that the motor can be driven by a n ion gradient; thus the mechanism may apply as well to the bacterial flagellar motor and to ATP synthase.