Mu is one of the 10 “Paradigm Phages” of E. coli, meaning that it has been the subject of extensive experimental investigation, mainly because it replicates by gene transposition; i.e., it is a transposon that hops from one DNA site to another every time it replicates its DNA. It is also the only Paradigm Phage for which the molecular mechanism of lysis is still largely a mystery. The Young lab has focused on lysis, the bursting event that terminates the bacteriophage infection cycle, for ~35 years, and during that period, has identified lysis genes and their molecular mechanisms that are thought to be essentially universal among phages. Normally, there is one protein, a membrane protein called the holin, that controls lysis by controlling the activity of an enzyme, called the endolysin, that degrades the host cell wall. In some phages, there is a second membrane protein called the antiholin that negatively regulates the holin. However, recently a Young lab graduate student did preliminary experiments knocking out Mu genes that were thought to be involved in lysis.
Bioinformatic analysis showed that there were three membrane proteins (see model of inner membrane, IM, topology of the proteins). Those knockouts showed that gene 19 encodes the holin, which was interesting because it was the first holin with four transmembrane domains. It also confirmed that gene 22 encoded the endolysin enzyme. Surprisingly, however, knockouts of gene 20 and gene 25, both encoding small membrane proteins, also had dramatic lysis phenotypes. The results suggest that an entirely new regulatory mechanism may be operating in Mu. With a new project leader, the Mu lysis project has many clear directions. The project would involve mutagenesis and engineering of phage Mu, as well as microbial physiology and analysis of the protein products of the suspected lysis genes. To complete some key experiments necessary for publication, the project would require at least two semesters.
Contact Jolene Ramsey, postdoctoral researcher if you are interested.