Host Takeover by Bacteriophage T4

National Institute Of Diabetes And Digestive And Kidney Diseases

Investigators

Linked publications & trials

Abstract

Phage genes of unknown function comprise an abundance of biological dark matter. Even in the well-studied phage T4, approximately 30% of the genome has not been functionally characterized. The T4 early, nonessential gene, motB, is one such gene. Although limited previous work suggested that motB might be involved in T4 gene expression, our previous RNA-seq analyses of a T4 motBam infection or of a T4 wt infection in E. coli with excess production of MotB indicates that MotB does not significantly affect the expression of phage RNA. However, the presence of motB increases phage burst 2-fold and production of MotB is highly toxic for E. coli. We have found that MotB is a tight DNA binding protein with no detectable sequence specificity and with similar affinities for unmodified host and modified (glucosylated, hydroxymethylated cytosines) T4 DNA. Our pull-down assays indicate that the E. coli histone-like protein H-NS, which is known to repress xenogenic sequences, co-purifies with MotB in the presence of DNA. In addition, RNA-seq analyses of E. coli gene expression in the presence of MotB reveals that a subset of H-NS-regulated host genes are differentially expressed. To investigate how MotB interacts with DNA in the presence or absence of H-NS, we have performed atomic force microscopy (AFM). As expected, H-NS forms filaments or bridges along the DNA. In contrast, MotB compacts the DNA in a novel manner, forming protein/DNA 'spaghetti monsters'. To investigate the effect of MotB production on the DNA in vivo, we heterologously produced MotB or MotB-GFP in E. coli or E. coli containing H-NS tagged with mcherry. We find that the presence of MotB results in significant cell lengthening and DNA compaction, consistent with the DNA compaction observed by AFM. Both MotB-GFP and H-NS-mcherry associate with the compacted DNA. We speculate that the presence of MotB may help T4 infection by sequestering H-NS, by extending the exponential phase of E. coli, by compacting the host DNA for more efficient cleavage or T4 DNA for more efficient packaging, and/or simply by providing more room for phage within the cell.