A New Small Low-Abundant Nonstructural Protein Encoded by the L Segment of the dsRNA Bacteriophage Φ6

Abstract

A new small low-abundant protein encoded by the large genome segment of bacteriophage Φ6 has been detected in extracts of Escherichia coli bearing Φ6 cDNA clones and in extracts of phage-infected Pseudomonas phaseolicola. This 62 amino acid protein, designated P14, has a net charge of +2 at pH 7.0. Gene 14 has been located by deletion analysis and N-terminal protein sequence. Expression of P14 is down-regulated in E. coli when the complete L segment clone is expressed. Polyclonal antibodies to P14 detected the new protein in small amounts in phage-infected cells but not in Φ6 virions or nucleocapsids, or in procapsids assembled in E. coli. Procapsids assembled in E. coli after expression of Φ6 L segment clones with or without gene 14 had essentially similar protein composition and activity in an in vitro packaging and replication system. Thus P14 does not appear to be essential for the structure or assembly of functional procapsids. P14 might, however, facilitate packaging in vivo. Alternatively this protein could play a role in repair of host membranes following vital penetration.