Prohead RNA of bacteriophage 029: size, stoichiometry and biolocal activity

We previously demonstrated (Guo et al., 1987. Nucl. Acids Res. 15, 7081-7090) that purified proheads ofbacteriophage )29 contain an RNA of 120 bases 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 429 relatives 421, 415 and SF5. The concentration dependence in the reconstitution of RNA-free proheads suggests that one copy ofthe 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.