Transposable Phage Mu

Abstract

Transposable phage Mu has played a major role in elucidating the mechanism of movement of mobile DNA elements. The high efficiency of Mu transposition has facilitated a detailed biochemical dissection of the reaction mechanism, as well as of protein and DNA elements that regulate transpososome assembly and function. The deduced phosphotransfer mechanism involves in-line orientation of metal ion-activated hydroxyl groups for nucleophilic attack on reactive diester bonds, a mechanism that appears to be used by all transposable elements examined to date. A crystal structure of the Mu transpososome is available. Mu differs from all other transposable elements in encoding unique adaptations that promote its viral lifestyle. These adaptations include multiple DNA (enhancer, SGS) and protein (MuB, HU, IHF) elements that enable efficient Mu end synapsis, efficient target capture, low target specificity, immunity to transposition near or into itself, and efficient mechanisms for recruiting host repair and replication machineries to resolve transposition intermediates. MuB has multiple functions, including target capture and immunity. The SGS element promotes gyrase-mediated Mu end synapsis, and the enhancer, aided by HU and IHF, participates in directing a unique topological architecture of the Mu synapse. The function of these DNA and protein elements is important during both lysogenic and lytic phases. Enhancer properties have been exploited in the design of mini-Mu vectors for genetic engineering. Mu ends assembled into active transpososomes have been delivered directly into bacterial, yeast, and human genomes, where they integrate efficiently, and may prove useful for gene therapy.

Transposition Behavior Revealed by High-Resolution Description of Pseudomonas Aeruginosa Saltovirus Integration Sites

“…For instance, the linear 37 kb Mu phage double-strand DNA genome is packaged with 50–150 base-pairs of DNA fragments of the E. coli host genome on the left side from which packaging is initiated [ 3 ] and a few hundred base-pairs up to 2–3 kb on the right side resulting from full-head packaging [ 4 ]. Two phage-coded proteins, MuA and MuB, are essential for Mu transposition (reviewed in References [ 5 , 6 ]). MuA, a DDE recombinase, binds to the phage attachment sites (attL and attR) and to the phage transposition enhancer region whereas MuB, an AAA+ ATPase binds nonspecifically to the host chromosome and is therefore involved in the selection of insertion sites [ 6 , 7 , 8 , 9 ].…”

Host factors that promote retrotransposon integration are similar in distantly related eukaryotes

“…One possibility is that MRX is important for repairing integration sites because it displaces IN. Studies of Mu phage show that the transpososome adheres tightly to integration sites and is removed by the ClpX protease [ 103 , 104 ].…”

Multiple serine transposase dimers assemble the transposon-end synaptic complex during IS607-family transposition

“…For example, each subunit of the Mos1 Mariner-family transposase dimer binds to one transposon terminus and additional separate DNA binding domains associate with two subterminal binding sites on the other transposon end within the active complex ( Richardson et al, 2009 ). Assembly of the phage Mu transpososome, which contains four copies of the Mu A protein, is more complex as it involves interactions with a remote enhancer-like element by a distinct DNA binding domain ( Harshey, 2014 ). hAT -family transposons often have many subterminal repeats at variable spacings and orientations, which in some elements, can be located hundreds of base pairs from the transposon termini ( Atkinson, 2015 ).…”