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Biomedical subjects

M Altschuler

Publications and source records attributed to M Altschuler.

12 recordsLinked to original sources
PubMed1997

Study to determine the ability of clinical laboratories to detect antimicrobial-resistant Enterococcus spp. in Buenos Aires, Argentina.

Few reports of vancomycin-resistant enterococci have appeared outside the USA. Therefore, we evaluated the ability of five laboratories in Buenos Aires, Argentina, to perform susceptibility testing using the disk diffusion method. Laboratories had difficulty identifying the low- and intermediate-level vancomycin-resistant phenotypes. This suggests that the disk diffusion method used by laboratories abroad may fail to detect some vancomycin-resistant enterococci.

Anti-Bacterial Agents↗
PubMed1995

Detection of cleavage products from an in vivo transcribed cis hairpin ribozyme in turnips using the CaMV plant virus.

In order to examine ribozyme (Rz) activity in vivo, we have adapted a virus to deliver Rz to plants. DNA fragments that code for both active and mutant cis-hairpin Rz were cloned into the double-stranded DNA plant virus, cauliflower mosaic virus (CaMV). These Rz constructs successfully infected Brassica campestris rapa (turnip). The plants that were infected with the active-Rz construct showed, on average, a one-week delay in the appearance of viral symptoms, when compared to the mutant-Rz control. Since CaMV replicates through reverse transcription of a full-length RNA intermediate, Rz cloned into the CaMV DNA should be transcribed within this viral RNA. If these Rz constructs cleave, the amount of intact virus RNA should be reduced, resulting in attenuated viral symptoms. In addition, lysate RNase protection assays showed fragments corresponding to the sizes of both the 5' and 3' cis cleavage products in the active Rz tissue. No cleavage products were observed from plant tissue infected with the mutant Rz. Both the attenuated systemic viral symptoms and the cleavage products from the protection assay strongly support in vivo transcription and cleavage of this hairpin Rz. This is the first report of an in vivo transcribed Rz showing cleaved products by direct RNA analysis (non-PCR) in plants or animals.

Base Sequence↗
PubMed1994

Alteration of hairpin ribozyme specificity utilizing PCR.

We have developed a method by which a researcher can quickly alter the specificity of a trans hairpin ribozyme. Utilizing this PCR method, two oligonucleotides, and any target vector, new ribozyme template sequences can be generated without the synthesis of longer oligonucleotides. We have produced templates with altered specificity for both standard and modified (larger) ribozymes. After transcription, these ribozymes show specific cleavage activity with the new substrate beta-glucuronidase (GUS), and no activity against the original substrate (HIV-1, 5' leader sequence). Utilizing this technique, it is also possible to produce an inactive ribozyme that can be used as an antisense control. Applications of this procedure would provide a rapid and economical system for the assessment of trans ribozyme activity.

Base Sequence↗
PubMed1993

Accumulation of type I fish antifreeze protein in transgenic tobacco is cold-specific.

Expression of fish antifreeze protein (AFP) genes in plants is a possible means of increasing their frost resistance and freeze tolerance. Initial work involved transfer into tobacco of an AFP gene from winter flounder which codes for the alanine-rich, alpha-helical Type I AFP. Plants were transformed with a gene construct in which the preproAFP cDNA was inserted between the cauliflower mosaic virus 19S RNA promoter and the nopaline synthetase polyadenylation site. Although transgenic plants produced AFP mRNA, no AFP was detected on western blots. Re-evaluation of AFP expression in these transgenic plants showed that AFP accumulated to detectable levels only after exposure of the plant to cold. Extracts of plants incubated at 4 degrees C for 24 h contained a protein which co-migrated with winter flounder proAFP and was cross-reactive to Type I AFP antisera. Two other minor protein bands of slightly higher apparent M(r) also cross-reacted with the antisera and are thought to represent processing intermediates. The proAFP was unique to the transgenic plants and was absent in extracts taken prior to cold exposure. AFP levels increased over the first 48 h of cold incubation then remained stable. Since the alpha-helix content of Type I AFP has been shown to decrease markedly at warmer temperatures, we postulate that Type I AFP stability in transgenic plants is dependent on its secondary structure.

Antifreeze Proteins↗
PubMed1993

Molecular cloning and expression of a MAP kinase homologue from pea.

The cdc2 kinases are important cell cycle regulators in all eukaryotes. MAP kinases, a closely related family of protein kinases, are involved in cell cycle regulation in yeasts and vertebrates, but previously have not been documented in plants. We used PCR to amplify Brassica napus DNA sequences using primers corresponding to amino sequences that are common to all known protein kinases. One sequence was highly similar to KSS1, a MAP kinase from Saccharomyces cerevisiae. This sequence was used to isolate a full-length MAP kinase-like clone from a pea cDNA library. The pea clone, called D5, shared approximately 50% amino acid identity with MAP kinases from yeasts and vertebrates and about 41% identity with plant cdc2 kinases. An expression protein encoded by D5 was recognized by an antiserum specific to human MAP kinases (ERKs). Messenger RNA corresponding to D5 was present at similar levels in all tissues examined, without regard to whether cell division or elongation were occurring in those tissues.

Amino Acid Sequence↗
PubMed1993

Alteration of gene expression by restriction enzymes electroporated into plant cells.

The alteration in the expression of a beta-glucuronidase (GUS) reporter gene was used to monitor the effect of restriction endonucleases electroporated into the tobacco (Nicotiana tabacum L.) protoplasts. Restriction enzyme (RE) Hind III which does not have a recognition site within the gene cassette, had little effect on enzyme activity. In contrast restriction endonucleases Hae III and Sau3A1 which possess 8 and 16 recognition sites in the GUS cassette, were found to reduce the enzyme activity by 89% and 94% respectively when compared to control electroporations. Restriction-site mutation analysis (RSM) and Southern blot analysis indicated the enzymatic degradation of GUS coding sequence by the REs Hae III and Sau3A1. Results of this study suggest that on electroporation, REs can enter into plant cells and alter the expression of the GUS gene. The alteration of gene expression is thus correlated with the digestion of GUS template DNA. Future applications of this technique could include addressing fundamental questions with regard to DNA repair, site-specific recombination, identifying mutations, insertional mutagenesis, enhancement of stable transformation and gene tagging in plants.

Base Sequence↗
PubMed1992

A method for generating transcripts with defined 5' and 3' termini by autolytic processing.

Plasmids containing both the hammerhead and hairpin ribozyme autocatalytic cassettes were constructed for the purpose of generating RNA transcripts with specific termini at both the 5' and 3' ends. Following transcription, the RNA encoded by these cassettes was capable of intramolecular cleavage. This resulted in the generation of a processed RNA, which was located between the two cassettes, with specifically engineered 5' and 3' ends. The two different ribozymes were selected for their efficient intramolecular cleavage ability and to reduce the possibility of DNA recombination that could occur if identical cassettes were used. An application of this technique was the generation of a processed RNA which was itself a ribozyme, with specific 5' and 3' termini. The ribozyme generated was a hairpin ribozyme specific for a sequence in the gene encoding hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCoA reductase). The processed ribozyme was fully catalytically active against an RNA substrate sequence of HMGCoA reductase.

Autolysis↗