This family includes PspA a protein that suppresses sigma54-dependent transcription. The PspA protein, a negative regulator of the Escherichia coli phage shock psp operon, is produced when virulence factors are exported through secretins in many Gram-negative pathogenic bacteria and its homologue in plants, VIPP1, plays a critical role in thylakoid biogenesis, essential for photosynthesis. Activation of transcription by the enhancer-dependent bacterial sigma(54) containing RNA polymerase occurs through ATP hydrolysis-driven protein conformational changes enabled by activator proteins that belong to the large AAA(+) mechanochemical protein family. It has been shown that PspA directly and specifically acts upon and binds to the AAA(+) domain of the PspF transcription activator [2].

1: The PspA protein of Escherichia coli is a negative regulator of sigma(54)-dependent transcription. Dworkin J, Jovanovic G, Model P; J Bacteriol 2000;182:311-319. PMID:10629175

2: Mechanism of Action of the Escherichia coli Phage Shock Protein PspA in Repression of the AAA Family Transcription Factor PspF. Elderkin S, Jones S, Schumacher J, Studholme D, Buck M; J Mol Biol 2002;320:23-37. PMID:12079332