YycH Regulates the Activity of the Essential YycFG Two-Component System in Bacillus subtilis

Abstract

Of the numerous two-component signal transduction systems found in bacteria, only a very few have proven to be essential for cell viability. Among these is the YycF (response regulator)-YycG (histidine kinase) system, which is highly conserved in and specific to the low-G؉C content gram-positive bacteria. Given the pathogenic nature of several members of this class of bacteria, the YycF-YycG system has been suggested as a prime antimicrobial target. In an attempt to identify genes involved in regulation of this two-component system, a transposon mutagenesis study was designed to identify suppressors of a temperature-sensitive YycF mutant in Bacillus subtilis. Suppressors could be identified, and the prime target was the yycH gene located adjacent to yycG and within the same operon. A lacZ reporter assay revealed that YycF-regulated gene expression was elevated in a yycH strain, whereas disruption of any of the three downstream genes within the operon, yycI, yycJ, and yycK, showed no such effect. The concentrations of both YycG and YycF, assayed immunologically, remained unchanged between the wild-type and the yycH strain as determined by immunoassay. Alkaline phosphatase fusion studies showed that YycH is located external to the cell membrane, suggesting that it acts in the regulation of the sensor domain of the YycG sensor histidine kinase. The yycH strain showed a characteristic cell wall defect consistent with the previously suggested notion that the YycF-YycG system is involved in regulating cell wall homeostasis and indicating that either up-or down-regulation of YycF activity affects this homeostatic mechanism.

Comparative analysis of two-component signal transduction systems of Bacillus cereus, Bacillus thuringiensis and Bacillus anthracis

“…An example of such a system might be YycHGF of B. subtilis. YycH, which is located external to the cell membrane, has been proposed to function as an extracellular sensor that confers its activity to the HK YycG (Szurmant et al, 2005). Another possibility is that the truncated HKs are relieved from sensory constraints and are therefore more active than their non-truncated orthologues.…”

Essentiality, Bypass, and Targeting of the YycFG (VicRK) Two-Component Regulatory System in Gram-Positive Bacteria

“…The best-studied example of cross talk in this system is between YycFG and the PhoPR phosphate limitation TCS in Bacillus subtilis (21,22). In addition, the YycFG TCS includes several auxiliary proteins in its complex regulatory circuits, making it in fact at least a four-component regulatory system in some bacterial species (34,45,46). However, recent studies have shown that there are instances where the YycFG TCS appears not to be essential in some bacterial systems (see below) (11,26,32).…”

“…1). The different names for the YycG and VicK histidine kinases coincide with different structural features (34,45,46,48) (Fig. 1).…”

A Life inBacillus subtilisSignal Transduction

“…Celine Fabret found a single system essential for growth whose transcription was repressed upon the initiation of sporulation (11). The genes for the kinase, YycG, and the response regulator, YycF, were in an operon with proteins of unknown function, YycI and YycH, later revealed to be activity regulators of YycG kinase, not transcription regulators (83). A temperature-sensitive YycF mutant stopped growth within 30 min, and microscopy revealed that cells were devoid of internal contents, suggesting leakage through the cell wall and membrane barriers.…”