Although the antibiotic thiostrepton is best known as an inhibitor of protein synthesis, it also, at extremely low concentrations (< 10-9 M), induces the expression of a regulon of unknown function in certain Streptomyces species. Here, we report the purification of a Streptomyces lividans thiostrepton-induced transcriptional activator protein, TipAL, whose N-terminus is similar to a family of eubacterial regulatory proteins represented by MerR.TipAL was first purified from induced cultures of S.lividans as a factor which bound to and activated transcription from its own promoter. The tipAL gene was overexpressed in Escherichia coli and TipAL protein purifi'ed in a single step using a thiostrepton affinity column. Thiostrepton enhanced binding of TipAL to the promoter and catalysed specific transcription in vitro.TipAs, a second gene product of the same open reading frame consisting of the C-terminal domain of TipAL, is apparently translated using its own in-frame initiation site. Since it is produced in large molar excess relative to TipAL after induction and also binds thiostrepton, it may competitively modulate transcriptional activation.

Bacteriophage #393-A2, isolated from an artisanal cheese whey sample, is a temperate phage able to generate stable lysogens through integration of its DNA into the bacterial genome. One-step growth kinetics of its lytic development revealed eclipse and latent periods of 100 and 140 min, respectively, with a burst size of about 200 p.f.u. per infected cell. #393-A2 virions have an isometric head and a long, non-contractile tail terminating in a baseplate. The capsid is composed of two major and at least nine minor structural polypeptides. The phage genome consists of a double-stranded DNA molecule of 44 kbp bearing 3'-protruding cohesive ends. A physical map of the phage DNA has been constructed for six restriction enzymes. The whole 4393-A2 genome has been cloned in Escherichia coli using plasmid-and phagederived cloning vectors.

Aims:The partial characterization of a bacteriocin produced by a human Lactobacillus delbrueckii isolate with probiotic potential. Methods and Results: A bacterocin, UO004, was partially puri®ed by cation exchange followed by a hydrophobic interaction column, biochemically characterized and the N-terminal region sequenced. Bacteriocin UO004 was found to be a hydrophobic, heat-stable polypeptide with an apparent molecular mass of 6 kDa. It was also stable and active over a wide pH range. Conclusions: The active compound was proteinaceous, heat-stable, and had a bactericidal (and bacteriolytic) mode of action on a limited number of micro-organisms. Such a narrow spectrum of activity is typical for bacteriocins produced by intestinal Lactobacillus. Signi®cance and Impact of the Study: Bacteriocin UO004 from a probiotic strain is a new compound that does not share any homology with any other known lactic acid bacteria bacteriocin. Furthermore, Lact. delbrueckii is regarded as a suitable starter for the production of fermented milks.

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activities have been detected in culture supernatant fluids of several Lactobacillus plantarum strains. In the case of Lact. plantarum HER 1325 at least, the extracellular activity is accompanied by a cytoplasmic restriction endonuclease. Among the secreted nucleases, the greatest activity was from Lact. plantarum ATCC 10241. This strain secretes an enzyme, with a molecular mass in the range 10-40 kDa, that cuts double-stranded DNA in a sequenceindependent way by initially introducing single-strand nicks in supercoiled molecules, followed by linearization and complete degradation of the substrate.