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Phosphate Control of the Biosynthesis of Antibiotics and Other Secondary Metabolites Is Mediated by the PhoR-PhoP System: an Unfinished Story. Juan F. Martín, 2004. Structure of the DNA-SspC Complex: Implications for DNA Packaging, Protection, and Repair in Bacterial Spores. Daphna Frenkiel-Krispin, 2004.Bacterial spores have long been recognized as the sturdiest known life forms on earth, revealing extraordinary resistance to a broad range of environmental assaults . A family of highly conserved spore-specific DNA-binding proteins, termed  /ß-type
small, acid-soluble spore proteins (SASP), plays a major role
in mediating spore resistance . The mechanism by which these proteins
exert their protective activity remains poorly understood, in part
due to the lack of structural data on the DNA-SASP complex . By using
cryoelectron microscopy, we have determined the structure of the
helical complex formed between DNA and SspC, a characteristic member
of the
/ß-type
SASP family . The protein is found to fully coat the DNA, forming
distinct protruding domains, and to modify DNA structure such that it
adopts a 3.2-nm pitch . The protruding SspC motifs allow for
interdigitation of adjacent DNA-SspC filaments into a tightly packed
assembly of nucleoprotein helices . By effectively sequestering DNA
molecules, this dense assembly of filaments is proposed to enhance
and complement DNA protection obtained by DNA saturation with the
/ß-type
SASP .
Effects of the P1 Plasmid Centromere on Expression of P1 Partition Genes. Jian-Jiang Hao, 2002.The partition operon of P1 plasmid encodes two proteins, ParA and ParB, required for the faithful segregation of plasmid copies to daughter cells . The operon is followed by a centromere analog, parS, at which ParB binds . ParA, a weak ATPase, represses the par promoter most effectively in its ADP-bound form . ParB can recruit ParA to parS, stimulate its ATPase, and significantly stimulate the repression . We report here that parS also participates in the regulation of expression of the par genes . A single chromosomal parS was shown to augment repression of several copies of the par promoter by severalfold . The repression increase was sensitive to the levels of ParA and ParB and to their ratio . The increase may be attributable to a conformational change in ParA mediated by the parS-ParB complex, possibly acting catalytically . We also observed an in cis effect of parS which enhanced expression of parB, presumably due to a selective modulation of the mRNA level . Although ParB had been earlier found to spread into and silence genes flanking parS, silencing of the par operon by ParB spreading was not significant . Based upon analogies between partitioning and septum placement, we speculate that the regulatory switch controlled by the parS-ParB complex might be essential for partitioning itself . Yeast Two-Hybrid Studies on Interaction of Proteins Involved in Regulation of Nitrogen Fixation in the Phototrophic Bacterium Rhodobacter capsulatus. Alice Pawlowski, 2003.Rhodobacter capsulatus contains two PII-like proteins, GlnB and GlnK, which play central roles in controlling the synthesis and activity of nitrogenase in response to ammonium availability . Here we used the yeast two-hybrid system to probe interactions between these PII-like proteins and proteins known to be involved in regulating nitrogen fixation . Analysis of defined protein pairs demonstrated the following interactions: GlnB-NtrB, GlnB-NifA1, GlnB-NifA2, GlnB-DraT, GlnK-NifA1, GlnK-NifA2, and GlnK-DraT . These results corroborate earlier genetic data and in addition show that PII-dependent ammonium regulation of nitrogen fixation in R . capsulatus does not require additional proteins, like NifL in Klebsiella pneumoniae . In addition, we found interactions for the protein pairs GlnB-GlnB, GlnB-GlnK, NifA1-NifA1, NifA2-NifA2, and NifA1-NifA2, suggesting that fine tuning of the nitrogen fixation process in R . capsulatus may involve the formation of GlnB-GlnK heterotrimers as well as NifA1-NifA2 heterodimers . In order to identify new proteins that interact with GlnB and GlnK, we constructed an R . capsulatus genomic library for use in yeast two-hybrid studies . Screening of this library identified the ATP-dependent helicase PcrA as a new putative protein that interacts with GlnB and the Ras-like protein Era as a new protein that interacts with GlnK .
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