PURIFICATION AND EXPRESSION OF THE GENE-III PROTEIN FROM FILAMENTOUS PHAGE PHI-LF

The gene III protein (pIII) from phi Lf, a filamentous phage of Xantho monas campestris pv. campestris, was purified by gel filtration with F PLC. The gIII coding region was amplified by PCR, which was then clone d into pUC18 and expressed in Escherichia coli. The size of both pIII, purified from phage particle and expressed in E. coli, is similar to the value deduced from the nucleotide sequence as shown by Western blo t analysis. This is different from the case in Ff phages (f1, fd, and M13), in which the size of pIII observed in SDS-polyacrylamide gel ele ctrophoresis is substantially larger than the deduced value. Upon infe ction of X. c. pv. vesicatoria carrying cloned phi LfgIII with phi Xv, a filamentous phage of pv. vesicatoria, the progeny particles in supe rnatant were able to infect both pv. campestris carrying cloned phi Lf gIII and pv. vesicatoria, indicating that a mixture of authentic phi X v and chimeric phage consisting of phi Xv DNA and phi LfpIII was produ ced. These results suggest pIII to be the adsorption protein required for host recognition. (C) 1998 Academic Press.