Prohead RNA of bacteriophageπ29: size, stoichiometry and biological activity

Abstract

We previously demonstrated (Guo et al., 1987. Nucl. Acids Res. 15, 7081-7090) that purified proheads of bacteriophage .vphi.29 contain an RNA of 120 cases which is essential for DNA packaging. Here we report that this RNA exists primarily as a polymer of ca. 174 residues in phage-infected cells and that ca. 54 bases are cleaved from its 3''-terminus by adventitious nucleases during the purification of proheads. The long and short forms of the RNA had similar activity in in vitro DNA packaging and phage assembly. We report the sequence of the long form of the RNA and show that similar long and short forms can be isolated from the proheads of the .vphi. relatives .vphi.21, .vphi.15 and SF5. The concentration dependence in the reconstutition of RNA-free proheads suggests that one copy of the RNA is sufficient to restore DNA packaging activity to RNA-free proheads suggests that one copy of the RNA is sufficient to restore DNA packaging activity to RNA-free proheads. However, quantitative measurements indicate that 5 to 6 copies of the RNA are present on proheads isolated from phage-infected cells.