Sequence-induced DNA curvature at the bacteriophage lambda origin of replication.

DNA replication in bacteriophage lambda begins at a unique origin between residues 39,000 and 39,200 of the lambda genome. This segment of DNA serves a dual function since it also lies within the coding sequence of the lambda replication initiator protein O which binds origin DNA. The lambda origin sequence contains four 19-base-pair (bp) segments (iterons) which have dyad symmetry, followed by a 40-bp A + T-rich zone of highly asymmetrical base composition. It was noted earlier that lambda origin DNA exhibits an anomalous electrophoretic mobility on gels; that is, the length of DNA as determined by DNA sequencing is approximately 20% less than is predicted from electrophoretic mobility. Recent studies of kinetoplast minicircle DNA (K-DNA) from the protozoan Leishmania tarentolae have led to the proposal that sequence-induced DNA curvature could account for such electrophoretic anomalies by alteration of the shape of the DNA molecule. We now present evidence that the lambda origin contains a static curve.