Beschreibung:
<jats:p>Using a modification of the solid‐phase radioimmune assay of Broome and Gilbert [<jats:italic>Proc. Natl Acad. Sci. USA, 75</jats:italic>, 2746 (1978)] to screen the plaques of λ recombinant phages for the presence of an elevated level of helicase‐II‐specific antigen, we have identified the gene for helicase II in a library of <jats:italic>Escherichia coli</jats:italic> DNA. The DNA selected was subcloned from λ into plasmid vectors; restriction analysis located the DNA region encoding helicase II in a <jats:italic>Pvu</jats:italic>II fragment identical in size (2900 base pairs) and restriction pattern to that which contains the <jats:italic>uvrD</jats:italic> gene. Plasmids carrying this DNA fragment complemented the increased sensitivity to ultraviolet irradiation and the mutator phenotype of <jats:italic>uvrD</jats:italic> mutants. Furthermore, <jats:italic>uvrD502</jats:italic> mutant cells were found to liberate no helicase II activity upon extraction. Following transformation with the cloned DNA, active helicase II was recovered from the mutant cells. These results support the view that helicase II is encoded by <jats:italic>uvrD</jats:italic>.</jats:p>