Head morphogenesis genes of the Bacillus subtilis Bacteriophage SPP1

Abstract We have identified and characterized the phage cistrons required for assembly of SPP1 heads. A DNA fragment containing most of the head morphogenesis genes was cloned and sequenced. The 3′-end of a previously identified gene (gene 6 ) and eight complete open reading frames ( 7 to 15 ) were predicted. We have assigned genes 7 , 8 , 9 , 11 , 12 , 13 , 14 and 15 to these orf s by correlating genetic and immunological data with DNA and protein sequence information. G 7 P was identified as a minor structural component of proheads and heads, G 11 P as the scaffold protein, G 12 P and G 15 P as head minor proteins and G 13 P as the coat protein. Characterization of intermediates in head assembly, which accumulate during infection with mutants deficient in DNA packaging or in morphogenetic genes, allowed the definition of the head assembly pathway. No proteolytic processing of any of the head components was detected. Removal of G 11 P by mutation leads to the accumulation of prohead-related structures and aberrant particles which are similar to the assemblies formed by purified G 13 P in the absence of other phage-encoded proteins. The native molecular masses of G 11 P and G 13 P are about 350 kDa and larger than 5000 kDa, respectively (predicted molecular masses 23.4 kDa and 35.3 kDa, respectively). G 13 P, upon denaturation and renaturation, assembles from protomers into some prohead-related structures. The organization of the DNA packaging and head genes of SPP1 resembles the organization of genes in the analogous regions of phage λ and P22.