The genes encoding Hfq-dependent sRNAs possess a typical Rho-independent transcription terminator. Here, we have studied the molecular events occurring at Rho-independent terminators of sRNA genes, focusing on two well-characterized Hfq-binding sRNAs, SgrS and RyhB. We constructed several hybrid genes in which the DNA sequence corresponding to a strong Rhoindependent terminator was placed just downstream from the Rho-independent terminators of sRNA genes. By using this system, we demonstrate that transcripts frequently read through the Rho-independent terminators of sgrS and ryhB in normally growing cells. We show that Hfq does not affect the transcriptional readthrough event itself. We also find that the readthrough products no longer bind to Hfq in vivo. We have developed a competition assay based on a biotin-streptavidin system to analyze the interaction of Hfq and a particular RNA molecule in vitro. By using this method, we verify that the 3 ′ -extended form of SgrS does not bind to Hfq in vitro. Finally, we demonstrate that transcription termination is significantly enhanced under stress conditions where transcription initiation of sRNA genes on the chromosome is induced. We conclude that the production of sRNAs is regulated not only at the step of transcription initiation but also at the step of transcription termination. The mechanism by which transcription termination is enhanced under stress conditions remains to be understood.

The reaction of selenobenzophenones with diazomethane afforded the corresponding diarylethylenes and symmetrical olefins. The reaction with diaryldiazomethanes gave three different types of tetraarylethylenes. This reaction proceeded through 1,3,4‐selenadiazoline intermediates, and retrocyclization was observed. The formation of 1,3,4‐selendiazolines was independently confirmed by the reaction of benzophenone hydrazones with diselenium dibromide, which afforded tetraarylethylenes in good yields. This method is applicable to the two‐step synthesis of tetraarylethylenes from benzophenones. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

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Reaction of p-tolualdehyde hydrazone with disulfur dichloride in the presence of DBU gave 2,5-di (p-tolyl)-1,3,4-thiadiazole (1a) in 54% yield. Phenyldiazomethane also reacted with disulfur dichloride to afford 2,5-diphenyl-1,3,4-thiadiazole (1b) in 80% yield.