The amino terminus of the bacteriophage D108 transposase protein contains a two-component sequence-specific DNA-binding domain.

We have cloned various amino-terminal domains of the transposable bacteriophage D108 A protein (transposase) into a high-copy-number expression vector and visualized the D108 polypeptides and fusion proteins expressed by the recombinant plasmids. By using crude protein extracts made from strains harboring these recombinant plasmids, we have performed band competition assays and DNasel footprinting on a 32P-end-labeled DNA restriction fragment which contained the Mu right end (to which the Mu A protein binds) and have shown that these fusion proteins in crude extracts can specifically bind to this DNA substrate. Furthermore, we have divided the amino-terminal 13 kDa of the D108 A protein (which may contain two bi-alpha-helical protein structures) in half and have shown that each half is capable of independent binding to the Mu attR site. These results suggest that the D108 transposase protein contains multiple DNA-binding domains which may be required for the complex protein-DNA interactions of D108 transposition.