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K M Mayer

Publications and source records attributed to K M Mayer.

6 recordsLinked to original sources
PubMed1999

A mutation in the flanking 5'-TA-3' dinucleotide prevents excision of an internal eliminated sequence from the Paramecium tetraurelia genome.

The germline chromosomes in Paramecium and other ciliated protozoa contain regions of DNA that are excised and eliminated during the development of a new macronuclear genome. Paramecium tetraurelia internal eliminated sequences (IESs) are invariably flanked by a 5'-TA-3' dinucleotide sequence that is part of a larger 8-bp terminal inverted-repeat consensus sequence. Both features, the absolutely conserved 5'-TA-3' and the remaining 6-bp terminal inverted repeat, are shared with the mariner/Tc1 class of transposons. In this article we describe a mutant cell line (AIM-2) defective in excision of a single IES from the coding region of the A51 surface antigen gene. Excision of the 370-bp IES6649 is prevented by a single A to G transition in the invariably conserved 5'-TA-3' dinucleotide. Failure to excise IES6649 also revealed a 29-bp IES located inside IES6649. Additional experiments with the previously isolated AIM-1 mutant, which also contains an internal IES, shows that alternate excision using the wild-type end of IES2591 with an end from the internal IES is extremely rare or nonexistent. These results indicate that IESs are discrete elements whose excision depends upon nucleotides located within the consensus sequence, but also suggest that additional information is required to match one end of an IES with its excision partner.

Animals↗
PubMed1998

A mutation in Paramecium tetraurelia reveals functional and structural features of developmentally excised DNA elements.

The excision of internal eliminated sequences (IESs) from the germline micronuclear DNA occurs during the differentiation of a new macronuclear genome in ciliated protozoa. In Paramecium, IESs are generally short (28-882 bp), AT rich DNA elements that show few conserved sequence features with the exception of an inverted-terminal-repeat consensus sequence that has similarity to the ends of mariner/Tcl transposons (KLOBUTCHER and HERRICK 1995). We have isolated and analyzed a mutant cell line that cannot excise a 370-bp IESs (IES2591) from the coding region of the 51A variable surface protein gene. A single micronuclear C to T transition within the consensus sequence prevents excision. The inability to excise IES259 I has revealed a 28-bp IES inside the larger IES, suggesting that reiterative integration of these elements can occur. Together, the consensus sequence mutation and the evidence for reiterative integration support the theory that Paramecium IESs evolved from transposable elements. Unlike a previously studied Paramecium IES, the presence of this IES in the macronucleus does not completely inhibit excision of its Mild-type micronuclear copy through multiple sexual generations.

Animals↗
PubMed1998

Genetic mapping of Hessian fly avirulence gene vH6 using bulked segregant analysis.

The Hessian fly, Mayetiola destructor (Say), an important insect pest of wheat, Triticum aestivum L., has a gene-for-gene relationship with wheat: single genes in the insect condition avirulence to specific resistance genes in wheat. We report the discovery of the first molecular genetic marker that is tightly linked to a Hessian fly avirulence gene. This dominant DNA polymorphism (OPG15-1) was identified using bulked segregant analysis and arbitrary primers in polymerase chain reactions. Bulked segregant analysis was modified to accommodate the anomalous chromosome cycle of the Hessian fly. It was used to identify DNA polymorphisms linked to the gene (vH6) that confers avirulence to the resistance gene H6 in wheat. OPG15-1 was cloned and sequenced, and a pair of site-specific primers were designed that converted it into a codominant single-stranded conformational polymorphism. Both OPG15-1 and vH6 were shown to be X-linked, and the genetic distance between the two loci was 2.5 +/- 2.5 cM. In situ hybridization to polytene chromosomes of larval salivary glands indicated that OPG15-1 resides near the centromere of Hessian fly chromosome X1.

Animals↗
PubMed1995

Dose-response studies of MeIQx in rat liver and liver DNA at low doses.

2-Amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) is a heterocyclic amine mutagen found in cooked meats and is carcinogenic in mice and rats at high doses (mg/kg body wt). Humans, however, are exposed to low amounts (p.p.b.) in the diet, and the effects caused by exposure to human equivalent doses of MeIQx have been difficult to determine accurately. We report on the effect of MeIQx exposure on liver bioavailability, hepatic DNA binding and MeIQx persistence in both liver tissue and liver DNA after acute (24 h), and subchronic (7 day and 42 day) exposures in male Sprague-Dawley rats. Male Sprague-Dawley rats were administered [2-14C]MeIQx either by gavage or in the diet for 1, 7 or 42 days (1 x 10(-6) mg/kg day up to 3.4 x 10(-2) mg/kg day dose) and the [2-14C]MeIQx was measured by accelerator mass spectrometry (AMS). Assessment of the kinetics of hepatic MeIQx DNA adduct formation over 42 days (1.1 x 10(-4) mg [2-14C]MeIQx kg daily dose) shows that steady-state [2-14C]MeIQx tissue concentrations of 138 +/- 15 pg/g liver and DNA adduct levels of 113 +/- 10 ag adduct/micrograms DNA were reached at 14-28 days and 28 days respectively. The relationship between administered dose and either hepatic MeIQx DNA adduct levels or MeIQx tissue levels are linear for the 24 h, 7 day and 42 day exposures. Furthermore, MeIQx adducts persist for at least 14 days after exposure ceases. These data suggest that bioavailability and DNA adduction by MeIQx increase linearly with increasing dose for both acute and subchronic exposures. These data also show that MeIQx DNA adducts are useful in predicting daily exposure and support a linear extrapolation in the risk assessment of MeIQx. However, the quantitative relationship between DNA adducts and tumor formation will also depend on the specific tissue and the subsequent steps needed for tumor progression.

Animals↗
PubMedDate not supplied

The human lck cDNA clone YT16 is a transforming oncogene.

The lck gene belongs to the src gene family and it is implicated in processes of lymphomagenesis. A full-:length lck-encoding cDNA clone, termed YT16 was isolated from a subtractive cDNA library, which was specific for expressed genes of the human Jurkat T-cell lymphoma. Sequence analysis of this molecular clone revealed major structural alterations compared to other tyrosine kinases classified as src-related genes. Firstly, a region within thw YT16 sequence surrounding the conserved ATP-binding site was modified by several short frameshift mutations. Secondly, the regulatory important tyrosine-505 residue was substituted by a threonine at this aligned position. The latter mutation was expected to result in a constitutional hypophosphorylated and thus permanently activated protein tyrosine kinase. These significant genetic alterations within the coding region of YT16 prompted us to investigate its biological relevance in vivo. To this end, we expressed YT16-specific sequences in NIH 3T3 fibroblasts and looked for morphological transformation of transfected cells. Here we report, that transformation of NIH 3T3 cells is obtained, provided that inhibitory untranslated sequences are removed from the YT16 cDNA clone. These results lend support to the notion, that structurally altered lck genes, in this study represented by the YT16 clone, may contribute to neoplastic processes in lymphoid cells.

3T3 Cells↗