Assembly of Bacillus subtilis Phage Phi29. 2. Mutants in the Cistrons Coding for the Non-structural Proteins

Abstract

The effect on phage morphogenesis of sus mutations in the cistrons coding for nonstructural proteins was studied. Mutants in 3 cistrons analyzed that are involved in phage DNA synthesis, and in cistron 16 which codes for a late nonstructural protein, produce prolate capsids which are more rounded at the corners than complete phage heads and have an internal core; they contain the head proteins, the upper collar protein and protein p7, not present in mature phage particles. Mutants in cistron 7 do not produce capsids nor other phage-related structures; this result and the presence of p7 in phage capsids suggest an essential role in capsid assembly for this protein. The protein product of cistron 13 is probably needed for a stable DNA encapsulation, since mutants in this cistron produce mainly DNA-free complete phage particles and only .apprx. 10% of uninfective DNA-containing complete phage. Cistron 15 codes for a late, partially dispensable, nonstructural protein which is present in the DNA-free capsids produced after infection with the delayed-lysis mutant sus14(1242), used as the wild-type control, or with mutants in cistrons 9, 11, 12 and 13. Proteins p15 and p16 are probably involved in the encapsulation of viral DNA in a prohead.