The E-coli Global Regulator DksA Reduces Transcription during T4 Infection

Bacteriophage T4 relies on host RNA polymerase to transcribe three promoter classes: early (Pe, requires no viral factors), middle (Pm, requires early proteins MotA and AsiA), and late (Pl, requires middle proteins gp55, gp33, and gp45). Using primer extension, RNA-seq, RT-qPCR, single bursts, and a semi-automated method to document plaque size, we investigated how deletion of DksA or ppGpp, two E. coli global transcription regulators, affects T4 infection. Both ppGpp(0) and Delta dksA increase T4 wild type (wt) plaque size. However, ppGpp(0) does not significantly alter burst size or latent period, and only modestly affects T4 transcript abundance, while Delta dksA increases burst size (2-fold) without affecting latent period and increases the levels of several Pe transcripts at 5 min post-infection. In a T4motA(am) infection, Delta dksA increases plaque size and shortens latent period, and the levels of specific middle RNAs increase due to more transcription from Pe's that extend into these middle genes. We conclude that DksA lowers T4 early gene expression. Consequently, Delta dksA results in a more productive wt infection and ameliorates the poor expression of middle genes in a T4motA(am) infection. As DksA does not inhibit Pe transcription in vitro, regulation may be indirect or perhaps requires additional factors.