The 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 global transcription regulators, affects T4 infection. Both ppGpp⁰ and Δ increase T4 wild type (wt) plaque size. However, ppGpp⁰ does not significantly alter burst size or latent period, and only modestly affects T4 transcript abundance, while Δ increases burst size (2-fold) without affecting latent period and increases the levels of several Pe transcripts at 5 min post-infection. In a T4 infection, Δ 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, Δ results in a more productive wt infection and ameliorates the poor expression of middle genes in a T4 infection. As DksA does not inhibit Pe transcription in vitro, regulation may be indirect or perhaps requires additional factors.