Genome-wide analysis of intracellular pH reveals quantitative control of cell division rate by pHc in Saccharomyces cerevisiae.

BACKGROUND: Because protonation affects the properties of almost all molecules in cells, cytosolic pH (pH(c)) is usually assumed to be constant. In the model organism yeast, however, pH(c )changes in response to the presence of nutrients and varies during growth. Since small changes in pH(c )can lead to major changes in metabolism, signal transduction, and phenotype, we decided to analyze pH(c )control. RESULTS: Introducing a pH-sensitive reporter protein into the yeast deletion collection allowed quantitative genome-wide analysis of pH(c )in live, growing yeast cultures. pH(c )is robust towards gene deletion; no single gene mutation led to a pH(c )of more than 0.3 units lower than that of wild type. Correct pH(c )control required not only vacuolar proton pumps, but also strongly relied on mitochondrial function. Additionally, we identified a striking relationship between pH(c )and growth rate. Careful dissection of cause and consequence revealed that pH(c )quantitatively controls growth rate. Detailed analysis of the genetic basis of this control revealed that the adequate signaling of pH(c )depended on inositol polyphosphates, a set of relatively unknown signaling molecules with exquisitely pH sensitive properties. CONCLUSIONS: While pH(c )is a very dynamic parameter in the normal life of yeast, genetically it is a tightly controlled cellular parameter. The coupling of pH(c )to growth rate is even more robust to genetic alteration. Changes in pH(c )control cell division rate in yeast, possibly as a signal. Such a signaling role of pH(c )is probable, and may be central in development and tumorigenesis

YidC and SecY mediate membrane insertion of a type I transmembrane domain

YidC has been identified recently as an evolutionary conserved factor that is involved in the integration of inner membrane proteins (IMPs) in Escherichia coli. The discovery of YidC has inspired the reevaluation of membrane protein assembly pathways in E. coli. In this study, we have analyzed the role of YidC in membrane integration of a widely used model IMP, leader peptidase (Lep). Site-directed photocross-linking experiments demonstrate that both YidC and SecY contact nascent Lep very early during biogenesis, at only 50-amino acid nascent chain length. At this length the first transmembrane domain (TM), which acquires a type I topology, is not even fully exposed outside the ribosome. The pattern of interactions appears dependent on the position of the cross-linking probe in the nascent chain. Upon elongation, nascent Lep remains close to YidC and comes into contact with lipids as well. Our results suggest a role for YidC in both the reception and lipid partitioning of type I TMs

Targeting, isertion and localization of E. coli YidC.

YidC was recently shown to play an important role in the assembly of inner membrane proteins (IMPs) both in conjunction with and separate from the Sec-translocon. Little is known about the biogenesis and structural and functional properties of YidC, itself a polytopic IMP. Here we analyze the targeting and membrane integration of YidC using in vivo and in vitro approaches. The combined data indicate that YidC is targeted by the signal recognition particle and inserts at the SecAYEG-YidC translocon early during biogenesis, unlike its mitochondrial homologue Oxalp. In addition, YidC is shown to be relatively abundant compared with other components involved in IMP assembly and is predominantly localized at the poles of the cell

Detection of cross-links between FtsH, YidC, HflK/C suggests a linked role for these proteins in quality control upon insertion of bacterial inner membrane proteins

Little is known about the quality control of proteins upon integration in the inner membrane of Escherichia coli. Here, we demonstrate that YidC and FtsH are adjacent to a nascent, truncated membrane protein using in vitro photo cross-linking. YidC plays a critical but poorly understood role in the biogenesis of E. coli inner membrane proteins (IMPs). FtsH functions as a membrane chaperone and protease. Furthermore, we show that FtsH and its modulator proteins HflK and HflC copurify with tagged YidC and, vice versa, that YidC copurifies with tagged FtsH. These results suggest that FtsH and YidC have a linked role in the quality control of IMPs

Hepatitis B screening among immigrants: How to successfully reach the Moroccan community

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