Biomedical subjects

S Kushnir

Publications and source records attributed to S Kushnir.

21 records · Page 2Linked to original sources

PubMed1994

The Arabidopsis thaliana apurinic endonuclease Arp reduces human transcription factors Fos and Jun.

An Arabidopsis thaliana cDNA encoding an analogue, referred to as Arp for apurinic endonuclease-redox protein, of the human redox factor REF has been cloned. Arp stimulates in vitro DNA-binding activity of the human transcription factor Jun and Fos by the reduction of a cysteine residue located in the DNA-binding domain. Based on amino acid sequence homology, this redox activity is probably confined to the small internal domain of the Arp protein. In analogy to REF, we show that the Arabidopsis Arp protein also functions as an apurinic/apyrimidinic class II endonuclease. This base-free endonuclease activity resides in the carboxyl-terminal domain, and this part of the protein has significant sequence similarity to bacterial (Escherichia coli exonuclease III and Streptococcus pneumoniae exonuclease A) and animal (Drosophila Rrp1 and human REF/HAP) apurinic/apyrimidinic endonucleases. The amino-terminal domain of the Arp protein is highly charged and apparently increases the affinity of the protein for DNA. Therefore, the Arabidopsis Arp protein is multifunctional and may be involved both in DNA repair and in the regulation of transcription.

Arabidopsis↗

PubMed1992

Suppression of beta-1,3-glucanase transgene expression in homozygous plants.

A chimeric construct containing the Nicotiana plumbaginifolia beta-1,3-glucanase gn1 gene was introduced into Nicotiana tabacum SR1 to produce high levels of the enzyme constitutively. We determined that the GN1 protein represents a basic beta-1,3-glucanase isoform which accumulates into the vacuoles of the transgenic plants. Analysis of the progeny of the transgenic plant with the highest levels of gn1 expression revealed an unexpected phenomenon of gene suppression. Plants hemizygous for the T-DNA locus contained high levels of gn1 mRNA and exhibited a 14-fold higher beta-1,3-glucanase activity than untransformed plants. However, the expression of gn1 was completely suppressed in the homozygous plants: no corresponding mRNA or protein could be detected. This suppression mechanism occurs at a post-transcriptional level and is under developmental control. In addition, by generating haploid plants we found that this silencing phenomenon is not dependent on allelic interaction between T-DNA copies present at the same locus of homologous chromosomes, but rather is correlated with the transgene dose in the plant genome. We postulate that high doses of GN1 protein relative to the level(s) of other still unknown plant products could trigger the cellular processes directed to suppress gn1 expression.

Blotting, Northern↗

PubMed1991

Nucleo-cytoplasmic incompatibility in cybrid plants possessing an Atropa genome and a Nicotiana plastome.

Twenty-nine cybrids possessing an Atropa belladonna nuclear genome and a Nicotiana tabacum plastome were selected from two independent protoplast fusion experiments. In contrast to the previously described reciprocal, green and fertile cybrids with a Nicotiana nuclear genome and an Atropa plastome (Kushnir et al. 1987), the plants obtained were totally chlorophyll-deficient. An Atropa nuclear genome and a Nicotiana plastome from these chlorophyll-deficient cybrids were combined with an Atropa or a Scopolia plastome and a Nicotiana nuclear genome, respectively, in control fusion experiments. All of these nuclear genome/plastome combinations gave rise to normal, green plants. Therefore, we conclude that an N. tabacum plastome is incompatible with an A. belladonna nuclear genome.

Amylases↗