A genetic screen for Caenorhabditis elegans mutants with enhanced susceptibility to killing by Pseudomonas aeruginosa led to the identification of two genes required for pathogen resistance: sek-1, which encodes a mitogen-activated protein (MAP) kinase kinase, and nsy-1, which encodes a MAP kinase kinase kinase. RNA interference assays and biochemical analysis established that a p38 ortholog, pmk-1, functions as the downstream MAP kinase required for pathogen defense. These data suggest that this MAP kinase signaling cassette represents an ancient feature of innate immune responses in evolutionarily diverse species.

The adcCBA putative operon of Streptococcus pneumoniae, an important human pathogen, was identified in a search for transformation-deficient mutants. It was found to exhibit homology to ATP-binding cassette (ABC) transport operons encoding streptococcal adhesins such as FimA of Streptococcus parasanguis and PsaA of S. pneumoniae. The latter was recently shown to be essential for virulence as judged by intranasal or intraperitoneal challenge of mice. We suggested previously that AdcA, together with a set of 14 proteins, including PsaA and homologous adhesins, defines a new family of external solute-binding proteins specific for metals. In this work, Northern analysis revealed the existence of two adcB-adcA specific transcripts originating within adcC or further upstream, consistent with the hypothesis that adc is an operon. Investigation of growth of adc and psaA mutants in synthetic medium revealed that the addition of Zn improved the growth rate of the former, whereas the latter exhibited an absolute requirement for added Mn. A psaA-adc double mutant turned out to be essentially non-viable unless both metals were added in the appropriate ratio. Taken together, these results suggest a previously undocumented requirement of S. pneumoniae for Zn and Mn. The addition of Zn also restored near-normal spontaneous transformation of adc mutant cells in standard transformation medium. Zn was found to be specifically required soon after contact of cells with the competence-stimulating peptide, revealing an unsuspected need for Zn in transformation of S. pneumoniae. The removal of Mn from standard transformation medium also resulted in transformation deficiency of psaA mutant cells. Taken together, these results lead us to propose that Adc is an ABC-type Zn permease, the first such protein complex identified in any organism, and that Psa is an ABC-type Mn permease complex.

We report the discovery of a group of highly conserved DNA sequences located, in those cases studied, within intergenic regions of the chromosome of the Gram positive Streptococcus pneumoniae. The S. pneumoniae genome contains about 25 of these elements called BOX. From 5' to 3', BOX elements are composed of three subunits (boxA, boxB, and boxC) which are 59, 45 and 50 nucleotides long, respectively. BOX elements containing one, two and four copies of boxB have been observed; boxB alone was also detected in one instance. These elements are unrelated to the two most thoroughly documented families of repetitive DNA sequences present in the genomes of enterobacteria. BOX sequences have the potential to form stable stem-loop structures and one of these, at least, is transcribed. Most of these elements are located in the immediate vicinity of genes whose product has been implicated at some stage in the process of genetic transformation or in virulence of S. pneumoniae. This location raises the intriguing possibility that BOX sequences are regulatory elements shared by several coordinately controlled genes, including competence-specific and virulence-related genes.