Novel Genetic Determinants for Complex Head Composition in a Giant Salmonella Phage

摘要

Mass spectrometry has played a pivotal role in defining the virion complexity of SPN3US, showing it uses up to 46% of its 240 kb genome to encode virion genes. This indicates SPN3US should be an excellent model phage to study the ΦKZ-related phage family, as 74% of its virion proteins have homologs in ΦKZ. The isolation and sequencing of SPN3US amber mutant phages identified 19 virion genes as being essential, which could not have been known from sequence-based searches. Our mass spectral analyses of two mutants (am11 and am27) have resulted in novel findings regarding giant phage head composition and assembly. Since the genes in these two mutants have homologs in all ΦKZ-related phages, these findings are relevant to all these phages and support SPN3US as an excellent model phage. Future work, we plan to continue to sequence our mutant phage collection to identify all the essential virion genes in SPN3US. We will also continue to analyze these mutants by MS (both their particles and in infected cells) to understand their role in giant phage virion composition and assembly. We are especially interested in head proteins that are ejected into the cell and their role in host takeover.