Phi 80 transcription antitermination complex: a 15 kDa host-coded protein interacts with the gene N transcription...

We purified the transcription antitermination complex of phi 80 (phi 80-pN complex). This complex had a molecular weight of approx. 42,000, and the subunits of this complex could be separated by SDS polyacrylamide gel electrophoresis. The complex was composed of two different polypeptides, one was the phi 80 N gene product (phi 80-pN) with a molecular weight of approx. 12,000, and the other was a host-coded protein with a molecular weight of approx. 15,000. The densitometric analysis after SDS polyacrylamide gel electrophoresis showed that the molar ratio of two proteins was 2 to 1 (phi 80-pN: 15 kDa), and the complex was assumed to be a trimer. Bacteriophage phi 80 could grow in nusA, nusC, and nusE mutants of Escherichia coli, but failed to grow in a nusB mutant. The molecular weight of the nusB gene product is calculated to be 15,689 from the sequencing data. These results suggest that the partner of the N gene product is possibly a host-coded nusB gene product.