Involvement of Streptococcus mutans regulator RR11 in oxidative stress response during biofilm growth and in the development of genetic competence.

AIMS: To identify the genes regulated by RR11, the regulator of the Streptococcus mutans HK/RR11 two-component system. METHODS AND RESULTS: The S. mutans RR11-encoding gene was inactivated, and the effects of gene disruption on the cell's ability to form biofilms under stresses and acquire extracellular DNA were tested. Biofilm was reduced in cells lacking RR11 following exposure to oxidative stress. RR11-defective cells showed approx. 20-fold reduction in transformation efficiency. Microarray used to decipher the RR11-regulated genes in biofilm showed that approx. 5% of the UA159 genome underwent a significant change in expression. RR11 was found to regulate 174 genes, including genes involved in competence, stress-response and cell division. CONCLUSIONS: Target genes controlled by RR11during biofilm growth have been identified by a comparison of transcriptional profiles between an RR11 defective mutant and the parental strain. The results demonstrated that RR11 is involved in the control of diverse cellular processes, including the formation of biofilm under oxidative stress and development of genetic competence. SIGNIFICANCE AND IMPACT OF THE STUDY: The regulator of HK/RR11 system controls a large regulon and is an important regulator involved in stress response during S. mutans biofilm growth enabling the survival and persistence of its progeny in the microbial community.

Gene expression analysis of the Streptococcus pneumoniae competence regulons by use of DNA microarrays.

Competence for genetic transformation in Streptococcus pneumoniae is coordinated by the competence-stimulating peptide (CSP), which induces a sudden and transient appearance of competence during exponential growth in vitro. Models of this quorum-sensing mechanism have proposed sequential expression of several regulatory genes followed by induction of target genes encoding DNA-processing-pathway proteins. Although many genes required for transformation are known to be expressed only in response to CSP, the relative timing of their expression has not been established. Overlapping expression patterns for the genes cinA and comD (G. Alloing, B. Martin, C. Granadel, and J. P. Claverys, Mol. Microbiol. 29:75-83, 1998) suggest that at least two distinct regulatory mechanisms may underlie the competence cycle. DNA microarrays were used to estimate mRNA levels for all known competence operons during induction of competence by CSP. The known competence regulatory operons, comAB, comCDE, and comX, exhibited a low or zero initial (uninduced) signal, strongly increased expression during the period between 5 and 12 min after CSP addition, and a decrease nearly to original values by 15 min after initiation of exposure to CSP. The remaining competence genes displayed a similar expression pattern, but with an additional delay of approximately 5 min. In a mutant defective in ComX, which may act as an alternate sigma factor to allow expression of the target competence genes, the same regulatory genes were induced, but the other competence genes were not. Finally, examination of the expression of 60 candidate sites not previously associated with competence identified eight additional loci that could be induced by CSP.

Global transposon mutagenesis and a minimal Mycoplasma genome.

Mycoplasma genitalium with 517 genes has the smallest gene complement of any independently replicating cell so far identified. Global transposon mutagenesis was used to identify nonessential genes in an effort to learn whether the naturally occurring gene complement is a true minimal genome under laboratory growth conditions. The positions of 2209 transposon insertions in the completely sequenced genomes of M. genitalium and its close relative M. pneumoniae were determined by sequencing across the junction of the transposon and the genomic DNA. These junctions defined 1354 distinct sites of insertion that were not lethal. The analysis suggests that 265 to 350 of the 480 protein-coding genes of M. genitalium are essential under laboratory growth conditions, including about 100 genes of unknown function.

Alanine scanning mutagenesis of conserved arginine/lysine-arginine/lysine-X-X-arginine/lysine G protein-activating motifs on m1 muscarinic acetylcholine receptors.

Alanine scanning mutagenesis of B-B-X-X-B motifis (where B is a basic residue and X is any nonbasic residue) in m1 muscarinic acetylcholine receptors was performed to determine the relative roles of basic amino acids in receptor coupling. This conserved motif is found in many G protein-coupled receptors and has been implicated in G protein activation. The KKAAR365 motif, located at the carboxyl-terminal third intracellular loop of m1 receptors, was mutated to AAAAA365, thereby generating a triple-substitution mutant devoid of ability to stimulate either phosphoinositide (PI) hydrolysis or cAMP accumulation. In contrast, a triple-alanine substitution of the KRTPR140 motif in the carboxyl-terminal second intracellular loop, yielding mutant AATPA140, had no effect on receptor coupling to the two independent second messenger pathways. Analysis of a series of single- and double-substitution mutants demonstrate that all three basic residues of the KKAAR365 motif participate in efficient m1 receptor coupling. The presence of second and third basic residues in this motif was absolutely critical for full agonist recognition of a high and low affinity state of the receptor. Mutation of either Lys362 or Lys365, but not-Lys361, abolished guanine nucleotide-dependent conversion of agonist affinity states and correlated with an inability of full agonists to fully activate PI hydrolysis. The different combinatorial double-substitution mutants also revealed that Lys365 was necessary but not sufficient, in the context of the KKAAR365 motif, for efficient receptor coupling. This residue cannot facilitate full agonist-stimulated Pl hydrolysis in the absence of both Lys361 and Lys362. In comparison, the critical residue Lys362 was both necessary and sufficient. Substitution of nearby basic residues Lys361 and Lys365 with alanine yielded mutant AKAAA365, which exhibited partial ability to couple PI hydrolysis after full agonist stimulation. Therefore, Lys365 seems to function in a hierarchal (interdependent) manner with nearby basic residues, whereas Lys361 and Lys362 can act independent of surrounding basic residues to facilitate partial m1 receptor coupling after full agonist stimulation. In contrast, all three residues must be present for stimulation of PI hydrolysis by a partial agonist.

Complete analysis of the presenilin 1 gene in early onset Alzheimer's disease.

The presenilin 1 gene has recently been identified as the locus on chromosome 14 which is responsible for a large proportion of early onset, autosomal dominantly inherited Alzheimer's disease (AD). We have elucidated the intron/exon structure of the gene and designed intronic primers to enable direct sequencing of the entire coding region (10 exons) of the presenilin gene in a large number of families. This strategy has enabled us to find a further two novel mutations in the gene. We discuss the distribution of mutations and the proportions of autosomal dominant AD with a mean age of onset below 60 years caused by mutations in this gene.