Morphogenesis of bacteriophage phi 29 of Bacillus subtilis: preliminary isolation and characterization of intermediate particles of the assembly pathway

Abstract

Three classes of particles were identified in restrictive .vphi.29 suppressor-sensitive (sus) mutant infections of B. subtilis, including DNA-containing heads or phage, proheads and empty heads. Pulse-chase labeling experiments indicate that the prohead, the 1st particle assembled in 14--infected cells, is converted to DNA-filled heads and .vphi.29. In addition to the proteins Hd, P10 and F found in mature .vphi.29, the prohead contains a core protein P7 that exits as the prohead matures and appears to recycle during subsequent rounds of prohead assembly. Prohead-like structures accumulate in UV-irradiated cells and are present in restrictive infections with sus mutants of cistrons 9 and 16. Empty heads are observed only when infection results in the formation of DNA-containing particles; the empty heads are probably not true intermediates. Phage .vphi.29 assembly apparently occurs by a single pathway in which neck and tail components interact to stablize the completed DNA-containing head.