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The type IC hsd loci of the enterobacteria are flanked by DNA with high homology to the phage P1 genome: implications for the evolution and spread of DNA restriction systems (1997)

Tyndall, Chiara ; Lehnherr, Hansjo¨rg ; Sandmeier, Ursula ; [et al.]

Oxford BSL : Blackwell Science Ltd

Molecular microbiology 23 (1997), S. 0

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ISSN: 1365-2958

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology , Medicine

Notes: EcoR124I, EcoDXXI and EcoprrI are the known members of the type IC family of DNA restriction and modification systems. The first three are carried on large, conjugative plasmids, while EcoprrI is chromosomally encoded. The enzymes are coded by three genes, hsdR, hsdM and hsdS. Analysis of the DNA sequences upstream and downstream of the type IC hsd loci shows that all are highly homologous to each other and also to sequences present in the bacteriophage P1 genome. The upstream sequences include functional phd and doc genes, which encode an addiction system that stabilizes the P1 prophage state, and extend to and beyond pac, the site at which phage DNA packaging begins. Downstream of the hsd loci, P1 DNA sequences begin at exactly the same place for all of the systems. For EcoDXXI and EcoprrI the P1 homology extends for thousands of base pairs while for EcoR124I an IS1 insertion and an associated deletion have removed most of the P1-homologous sequences. The significance of these results for the evolution of DNA restriction and modification systems is discussed.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1046/j.1365-2958.1997.2531622.x

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Molecular analysis of the Rhodobacter capsulatus chaperonin (groESL) operon: purification and characterization of Cpn60 (1996)

Hübner, Philipp ; Dame, Gregory ; Sandmeier, Ursula ; [et al.]

Springer

Archives of microbiology 166 (1996), S. 193-203

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ISSN: 1432-072X

Keywords: Key words GroEL ; GroES ; Protein purification ; ATPase activity ; Chaperonin activity ; Heat-shock ; induction ; Heat-shock promoter mapping ; Rhodobacter capsulatus

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract The heat-shock protein Cpn60 (chaperonin, GroEL homologue) from the phototrophic bacterium Rhodobacter capsulatus B10 was purified to homogeneity and biochemically characterized. Native Cpn60 from R. capsulatus was shown to be a tetradecamer of 840 kDa similar to that of homologous chaperones characterized so far. Cpn60 possesses ATPase activity and promotes refolding of chaotropically denatured citrate synthase. The groESL operon of R. capsulatus was cloned using a degenerate oligonucleotide and sequenced. Two open reading frames (285 and 1,635 bp) were found; they encode Cpn10 and Cpn60, with corresponding deduced molecular masses of 10.6 and 57.6 kDa. The deduced amino acid sequences coincided perfectly with those of the amino terminus and of three tryptic peptides of purified Cpn60 from R. capsulatus. Strong evidence that R. capsulatus encodes only one copy of the groESL operon was obtained. Primer-extension analysis revealed that the groESL operon is transcribed by a –35/–10-type promoter, and that transcription was initiated from the same positions before and after heat-shock under both chemotrophic and phototrophic conditions. The major initiation site is immediately followed by the inverted repeat structure CIRCE, which has been found upstream of many bacterial heat-shock operons. A second minor transcript starts just after the CIRCE element. Although heat-shock induction of a groEL-lacZ fusion failed because of thermal inactivation of the fusion protein, Western blot analysis revealed a two- to threefold induction of cellular Cpn60 levels 45–75 min after shifting from 28° C to 39° C. Deletion mapping of the groESL promoter identified upstream of the promoter a 19-bp element that enhances groESL transcription eightfold and contains the AT-rich sequence dAAATTTTT, which is found at similar positions in heat-shock operons of other gram-negative bacteria.