Characterization of the bacteriophage phi 29-encoded protein p16.7: a membrane protein involved in phage DNA replication

An early expressed operon, located at the right end of the linear bacteriop hage phi 29 genome, contains open reading frame (ORF)16.7, whose deduced pr otein sequence of 130 amino acids is conserved in phi 29-related phages. He re, we show that this ORF actually encodes a protein, p16.7, which is abund antly and early expressed after infection, p16.7 is a membrane protein, and the N-terminally located transmembrane-spanning domain is required for its membrane localization. The variant p16.7A, in which the N-terminal membran e anchor was replaced by a histidine-tag, was purified and characterized. P urified p16.7A was shown to form dimers in solution. To study the in vivo r ole of p16.7, a phi 29 mutant containing a suppressible mutation in gene 16 .7 was constructed. In vivo phage DNA replication was affected in the absen ce of p16.7, especially at early infection times. Based on the results, the putative role of p16.7 in in vivo phi 29 DMA replication is discussed.