Helicase-catalysed translocation and strand separation.

Helicases are molecular-motor enzymes that manipulate DNA or RNA during replication, repair, recombination, transcription, translation and processing of nucleic acids. The mechanisms for helicase activity have been studied intensely over the past decade. Recent advances in our understanding of the helicase mode of action have led to a general convergence of models that describe this diverse class of enzymes. One mechanism has been proposed that appears to have withstood the test of time, namely the inchworm mechanism. As the name implies, this mechanism involves a process whereby a helicase maintains at least two sites of contact with the nucleic acid. These binding sites can move relative to one another in a sequential fashion, resulting in net movement of the enzyme along the nucleic acid. The inchworm mechanism appears to be applicable to oligomeric states beyond the simple monomeric molecular motor. Although there are certainly many pertinent questions that remain unanswered, striking similarities in both form and function of seemingly disparate enzymes are becoming evident.