Cloning the complete rIIB gene of bacteriophage T4 and some observations concerning its middle promoters

We cloned the intact T4 rIIB gene by joining plasmids carrying gene fragments. rIIB was expressed at a low level under control of the lac promoter, and the clone complemented rIIB mutants. We suspect that earlier attempts to clone the intact gene were unsuccessful because of transcription from T4 middle-mode promoters. These promoters are silent early in infection but are recognized when resident on a plasmid in an uninfected cell.