Gerald B. Koudelka

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The repressor of phage 434 binds to six operator sites on the phage chromosome. A comparison of the sequences of these 14-base-pair (bp) operator sites reveals a striking pattern: at five of the six sites, the symmetrically arrayed outer eight base pairs (four in each half-site) are identical and the remaining site differs at only one position (Fig. 1b). In(More)
The bacteriophage 434 repressor regulates gene expression by binding with differing affinities to the six operator sites on the phage chromosome. The symmetrically arrayed outer eight base pairs (four in each half-site) of these 14-base-pair operators are highly conserved but the middle four bases are divergent. Although these four base pairs are not in(More)
In this review, we highlight recent work that has increased our understanding of the production and distribution of Shiga toxin in the environment. Specifically, we review studies that offer an expanded view of environmental reservoirs for Shiga toxin producing microbes in terrestrial and aquatic ecosystems. We then relate the abundance of Shiga toxin in(More)
UNLABELLED Phage-encoded Shiga toxin (Stx) acts as a bacterial defense against the eukaryotic predator Tetrahymena thermophila. It is unknown how Stx enters Tetrahymena protozoa or how it kills them. Tetrahymena protozoa are phagocytotic; hence, Stx could gain entry to the cytoplasm through the oral apparatus or via endocytosis. We find that Stx2 can kill(More)
The repressor of bacteriophage P22 (P22R) discriminates between its various DNA binding sites by sensing the identity of non-contacted base pairs at the center of its binding site. The "indirect readout" of these non-contacted bases is apparently based on DNA's sequence-dependent conformational preferences. The structures of P22R-DNA complexes indicate that(More)
The discovery of regulator and operator genes, summarized and organized into a model for repressive regulation by Jacob and Monod 1r1 in il6t, defined a fundamental logical circuitry for control of gene expreision. thai celebrated formulation is surely one of the great achievements of the first century of the Institut Pasteur. chemical entities that execute(More)
In a λ(imm434) lysogen, two proteins are expressed from the integrated prophage. Both are encoded by the same mRNA whose transcription initiates at the P(RM) promoter. One protein is the 434 repressor, needed for the establishment and maintenance of lysogeny. The other is Hex which is translated from an open reading frame that apparently partially overlaps(More)
The sequence of the bacteriophage 434 OR1 (ACAAAACTTTCTTGT) differs from its OR3 (ACAGTTTTCTTGT) at positions 4-6. X-ray analysis shows that the side chain of Gln33 of the 434 repressor makes van der Waals' and H-bond contacts with the T at position 4' in complex with OR1, but no specific contact is observed at this position in 434 repressor-OR3 complexes.(More)
We reported previously that 933W repressor apparently does not cooperatively bind to adjacent sites on DNA and that the relative affinities of 933W repressor for its operators differ significantly from that of any other lambdoid bacteriophage. These findings indicate that the operational details of the lysis-lysogeny switch of bacteriophage 933W are unique(More)