Identification of bacteriophage T4 gene 60 product and a role for this protein in DNA topoisomerase.

Bacteriophage T4 DNA topoisomerase has been isolated and shown to contain the proteins coded by the DNA-delay genes 39 and 52 (Liu, L. F., Liu, C.-C., and Alberts, B. M. (1979) Nature (Lond.) 281, 456-461 and Stetler, G. L., King, G. J., and Huang, W. M. (1979) Proc. Natl. Acad. Sci. U. S. A. 76, 3737-3741). From complementation measurements in vitro and from earlier genetic evidence, these workers suggested that the product of gene 60 (p60) was also a component of the DNA topoisomerase complex. This paper now establishes the identity of p60 and unequivocally shows that this protein is a component of the enzyme complex. T4 DNA topoisomerase was purified by a simplified two-column procedure and found to be a stable complex of p39, p52, and a protein with a relative molecular weight of 18,000. The 18,000-dalton chain has been unambiguously shown to be the product of gene 60 through the use of an amber mutant of gene 60 with Sup+ and Sup- hosts and analyses by two-dimensional gel electrophoresis. While p39 and p52 were tightly associated in the wild type enzyme complex, they were readily separated on a hydroxylapatite column from extracts of cells infected by an amber mutant of gene 60. These findings suggest that p60 plays a structural/functional role in the enzyme complex by holding the larger p39 and p52 in juxtaposition.