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Biomedical subjects

M Bölker

Publications and source records attributed to M Bölker.

24 records · Page 2Linked to original sources
PubMed1992

A two-component regulatory system for self/non-self recognition in Ustilago maydis.

In U. maydis the multiallelic b locus controls sexual and pathogenic development. In the b locus a gene coding for a regulatory protein had been identified, and it was suggested that the interaction of two b polypeptides specified by different alleles programs sexual development in this fungus. We now demonstrate the existence of a second regulatory gene in the b locus. We term this gene bW and refer to the former as the bE gene. Both genes exist in many alleles. Although unrelated in primary sequence, both genes are similar in their overall organization. The gene products display allele-specific variability in their N-terminal domains, show a high degree of sequence conservation in the C-terminal domains, and contain a homeodomain-related motif. Genetic evidence is provided to show that the pair of bE and bW polypeptides encoded by different b alleles is the key regulatory species.

Alleles↗
PubMed1992

The a mating type locus of U. maydis specifies cell signaling components.

The a mating type locus of the phytopathogenic fungus U. maydis controls fusion of haploid cells and filamentous growth of the dikaryotic mycelium. The a locus exists in two alleles, termed a1 and a2, which are defined by nonhomologous DNA regions comprising 4.5 kb for a1 and 8 kb for a2, flanked by identical sequences. Based on functional assays, mutants, and sequencing, we demonstrate that the mating type in each allele is determined by a set of two genes. One encodes a precursor for a lipopeptide mating factor, and the other specifies the receptor for the pheromone secreted by cells of opposite mating type. Thus, U. maydis employs a novel strategy to determine its mating type by providing the primary determinants of cell-cell recognition directly from the mating type locus.

Alleles↗
PubMed1989

Translation of the bacteriophage Mu mom gene is positively regulated by the phage com gene product.

Expression of the bacteriophage Mu mom gene is subject to posttranscriptional regulation by the phage com gene product. We have used mom-lacZ translational fusion genes to define the sequence requirements for stimulation of mom expression by Com. We show that the mom translation initiation region (TIR) is inactive in the absence of Com. We suggest that this repressed state is due to mRNA secondary structure in the TIR, since a deletion that destabilizes a stem-loop structure in the TIR results in high levels of Com-independent translation. We identify sequences on the mRNA, adjacent to the stem and loop, that are required for stimulation by Com. We propose that Com acts to stimulate initiation of translation by relieving the structural repression of the mom TIR. Indirect evidence is presented suggesting that Com binds to a site in the TIR.

Bacteriophage mu↗
PubMed1989

The Escherichia coli regulatory protein OxyR discriminates between methylated and unmethylated states of the phage Mu mom promoter.

Expression of the phage Mu mom gene is transcriptionally regulated by DNA methylation. Three GATC sites upstream of the mom promoter have to be methylated by the Escherichia coli deoxyadenosine methylase (Dam) to allow initiation of transcription. An E. coli dam strain was mutagenized with Tn5 in an attempt to isolate mutants which allow mom gene expression. Three independent Tn5 mutants were isolated, each mapped to a gene at 89.6 min which we designate momR. The wildtype gene was cloned and sequenced, it encodes a protein of 305 amino acids. The protein belongs to a group of related bacterial activators recently identified as the LysR family (Henikoff et al., 1988). MomR protein was overproduced and purified. Expression of momR is autoregulated; MomR binds to a 43 bp region upstream of its coding sequence. In the mom promoter MomR protects a 43 bp region containing the three GATC sites. Specific binding to these sequences was observed only with unmethylated DNA. Fortuitously, we learned that MomR is identical to OxyR, a regulatory protein responding to oxidative stress. We discuss the implications of this control for Mu development.

Amino Acid Sequence↗
PubMed1989

Role of bacteriophage Mu C protein in activation of the mom gene promoter.

The phage Mu C gene product is a specific activator of Mu late gene transcription, including activation of the mom operon. Fusion of the C gene to the efficient translation initiation region of the Escherichia coli atpE gene allowed significant overproduction of C protein, which was subsequently purified and assayed for DNA binding by gel retardation and nuclease footprinting techniques. C protein binds to a site immediately upstream of the -35 region both of the mom promoter and the related phage D108 mod promoter. The location of the mom promoter has been determined by primer extension. Upstream deletions extending more than 3 base pairs into the C-binding site abolished activation of the mom promoter in vivo. In vitro binding of C was not significantly affected by DNA methylation. A second, C-dependent promoter was identified just downstream of the C coding region; comparison with the mom promoter revealed common structural elements.

Amino Acid Sequence↗