Analysis of the kefA2 mutation suggests that KefA is a cation-specific channel involved in osmotic adaptation in Escherichia coli

Mechanosensitive channels play an essential role in the regulation of turgor pressure in bacteria. In Escherichia coli, there are multiple mechanosensitive channels that have been characterized genetically: MscL, YggB and KefA. In this report, we describe the cloning of the kefA gene, the organization of the KefA protein and the phenotype of a missense mutation, kefA, which affects the KefA mechanosensitive channel. The altered function of the channel is manifest through increased sensitivity to K+ during growth at low osmolarity and complete inhibition of growth in media containing high K+ concentrations (0.6 M) in the presence of betaine or proline. Growth in high Na+ medium (0.6 M NaCl plus 20 mM K+) is normal. Analysis of the cytoplasmic pools shows that the mutant cannot regulate the K+ content of the cytoplasm when grown in high K+ medium. However, regulation of pools of amino acids is essentially normal and the mutant can accumulate high pools of proline during growth inhibition. The mutant shows increased sensitivity to acid hypo-osmotic shock (transition from neutral to acid pH combined with a reduction in osmolarity). The data are consistent with abnormal regulation of KefA in the presence of high K+ concentrations and either betaine or proline.     

Aminoacyl-tRNA formation in the extreme thermophile Thermus thermophilus

Thermophilic organisms must be capable of accurate translation at temperatures in which the individual components of the translation machinery and also specific amino acids are particularly sensitive. Thermus thermophilus is a good model organism for studies of thermophilic translation because many of the components in this process have undergone structural and biochemical characterization. We have focused on the pathways of aminoacyl-tRNA synthesis for glutamine, asparagine, proline, and cysteine. We show that the T. thermophilus prolyl-tRNA synthetase (ProRS) exhibits cysteinyl-tRNA synthetase (CysRS) activity although the organism also encodes a canonical CysRS. The ProRS requires tRNA for cysteine activation, as is known for the characterized archaeal prolyl-cysteinyl-tRNA synthetase (ProCysRS) enzymes. The heterotrimeric T. thermophilus aspartyl-tRNA(Asn) amidotransferase can form Gln-tRNA in addition to Asn-tRNA: however, a 13-amino-acid C-terminal truncation of the holoenzyme A subunit is deficient in both activities when assayed with homologous substrates. A survey of codon usage in completed prokaryotic genomes identified a higher Glu:Gln ratio in proteins of thermophiles compared to mesophiles.     

The neural mechanisms of mate choice: a hypothesis

Scientists have described many physical and behavioral traits in avian and mammalian species that evolved to attract mates. But the brain mechanisms by which conspecifics become attracted to these traits is unknown. This paper maintains that two aspects of mate choice evolved in tandem: 1) traits that evolved in the "display producer" to attract mates and, 2) corresponding neural mechanisms in the "display chooser" that enable them to become attracted to these display traits. Then it discusses our (in-progress) fMRI brain scanning project on human romantic attraction, what we believe is a developed form of "courtship attraction" common to avian and mammalian species as well as the primary neural mechanism underlying avian and mammalian mate choice. The paper hypothesizes that courtship attraction is associated with elevated levels of central dopamine and norepinephrine and decreased levels of central serotonin in reward pathways of the brain. It also proposes that courtship attraction is part of a triune brain system for mating, reproduction and parenting. 1)The sex drive evolved to motivate birds and mammals to court any conspecifics. 2) The attraction system evolved to enable individuals to discriminate among potential mating partners and focus courtship activities on particular individuals, thereby conserving mating time and energy. 3) The neural circuitry for attachment evolved to enable individuals to complete species-specific parental duties.     

A novel colonic repressor element regulates intestinal gene expression by interacting with Cux/CDP

Intestinal gene regulation involves mechanisms that direct temporal expression along the vertical and horizontal axes of the alimentary tract. Sucrase-isomaltase (SI), the product of an enterocyte-specific gene, exhibits a complex pattern of expression. Generation of transgenic mice with a mutated SI transgene showed involvement of an overlapping CDP (CCAAT displacement protein)-GATA element in colonic repression of SI throughout postnatal intestinal development. We define this element as CRESIP (colon-repressive element of the SI promoter). Cux/CDP interacts with SI and represses SI promoter activity in a CRESIP-dependent manner. Cux/CDP homozygous mutant mice displayed increased expression of SI mRNA during early postnatal development. Our results demonstrate that an intestinal gene can be repressed in the distal gut and identify Cux/CDP as a regulator of this repression during development.     

Evidence of carpinus (betulaceae) in the late tertiary (pliocene) of alabama

Carpinus is a common and widespread element of the modern North American forest vegetation, but its scant fossil record on the continent is perplexing, especially considering the abundant and relatively continuous record of the genus in the Tertiary of Europe and Asia. Despite earlier claims of Tertiary Carpinus remains, recent reviews have indicated that a definitive post-Eocene Tertiary record of the genus in North America is lacking. Therefore, it remains uncertain if Carpinus was present but left no clear fossil record or if the genus became extinct in North America and migrated back to the continent more recently. A reinvestigation of the Citronelle Formation paleoflora has yielded conclusive evidence for the presence of Carpinus in the Gulf Coastal Plain of Alabama during the Pliocene based upon the discovery of a nutlet bract. Carpinus bracts are distinctive and consist of a central bract fused basally with two lateral bractlets. This specimen provides proof of the existence of Carpinus on this continent by the Pliocene Epoch, and any future research on the biogeography of the genus must consider this as the earliest, post-Eocene record of the genus in North America based on unequivocal reproductive structures.     

Activation of the pyrrolysine suppressor tRNA requires formation of a ternary complex with class I and class II lysyl-tRNA synthetases

Monomethylamine methyltransferase of the archaeon Methanosarcina barkeri contains a rare amino acid, pyrrolysine, encoded by the termination codon UAG. Translation of this UAG requires the aminoacylation of the corresponding amber suppressor tRNAPyl. Previous studies reported that tRNAPyl could be aminoacylated by the synthetase-like protein PylS. We now show that tRNAPyl is efficiently aminoacylated in the presence of both the class I LysRS and class II LysRS of M. barkeri, but not by either enzyme acting alone or by PylS. In vitro studies show that both the class I and II LysRS enzymes must bind tRNAPyl in order for the aminoacylation reaction to proceed. Structural modeling and selective inhibition experiments indicate that the class I and II LysRSs form a ternary complex with tRNAPyl, with the aminoacylation activity residing in the class II enzyme.