Serotonin induces four pharmacologically separable contractile responses in the pharynx of the leech Hirudo medicinalis.

Stimulation of the serotoninergic innervation of the leech pharynx or application of serotonin to the isolated pharynx induced four distinct types of contractile activity: an increase in basal tonus, large phasic contractions of 10-15 s in duration, smaller phasic contractions occurring at approximately 1 Hz, and a relaxation after washout of serotonin. Application to the isolated pharynx of the selective serotonin agonists (+/-)-8-hydroxy-2-(di-n-propylamino)tetralin, N-(3-trifluoromethylphenyl)piperazine, 1-(m-chlorophenyl)-piperazine, (+/-)-2,5-dimethoxy-4-iodoamphetamine, 2-methyl-5-hydroxytrypamine, alpha-methyl-5-hydroxytryptamine, and 5-methoxytryptamine induced distinct types of pharyngeal contractile activity. The results of this study suggest that the leech pharynx possesses more than one type of serotonin receptor.

Transcriptional regulation of the iron-responsive sigma factor gene pbrA.

In response to the intracellular iron concentration Pseudomonas fluorescens M114 coordinately regulates the production of pseudobactin M114, its cognate receptor PbuA, and a casein protease. Transcriptional initiation of this coordinate iron-stress response requires the sigma factor PbrA. PbrA is a member of the ECF (Extracytoplasmic function) subgroup of the sigma 70 family of eubacterial RNA polymerase sigma factors.

Isolation of a gene (pbsC) required for siderophore biosynthesis in fluorescent Pseudomonas sp. strain M114.

An iron-regulated gene, pbsC, required for siderophore production in fluorescent Pseudomonas sp. strain M114 has been identified. A kanamycin-resistance cassette was inserted at specific restriction sites within a 7 kb genomic fragment of M114 DNA and by marker exchange two siderophore-negative mutants, designated M1 and M2, were isolated.

Nucleotide sequence analysis and potential environmental distribution of a ferric pseudobactin receptor gene of Pseudomonas sp. strain M114.

The nucleotide sequence of the Pseudomonas sp. strain M114 pbuA gene, encoding the outer membrane receptor for ferric pseudobactin M114, has been determined. The region sequenced spans 2788 bases of plasmid pCUP3, within which the receptor gene had previously been localised.

Ammonia regulation of the Rhizobium meliloti nitrogenase structural and regulatory genes under free-living conditions: involvement of the fixL gene product?

The expression under microaerobic conditions of the Rhizobium meliloti nifA and consequently the nifHDK genes was found to be negatively regulated by ammonia and nitrate. Assimilation of the ammonia to glutamate and glutamine is not required for this regulation to occur. This indicates that ammonia itself, and not a product of its metabolism, may be regulating nif expression.

Regulation of iron assimilation: nucleotide sequence analysis of an iron-regulated promoter from a fluorescent pseudomonad.

An iron-regulated promoter was cloned on a 2.1 kb Bg/II fragment from Pseudomonas sp. strain M114 and fused to the lacZ reporter gene.