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Biomedical subjects

A Vassef

Publications and source records attributed to A Vassef.

10 recordsLinked to original sources
PubMed1988

Superiority of hemoglobin to hemin for cultivation of Leishmania tropica promastigotes in serum-free media.

Leishmania tropica promastigotes grew slowly but could be maintained for long periods in serum-free hemin-containing media formulated previously for other Leishmania species or in slightly simplified versions of these media. Replacement of hemin in the medium by hemoglobin resulted in a much longer log phase and a significant reduction in the doubling time. Cell counts in cultures started at 1 x 10(5) cells/ml increased 400-fold in less than 140 h in the hemoglobin-containing media. These media also proved suitable for growing L. donovani and L. enriettii promastigotes.

Animals↗
PubMed1987

Conserved sequences near the early transcription start sites of vaccinia virus.

Transcription start sites were determined for the herpes simplex virus thymidine kinase (HSV-TK) mRNA expressed by four vaccinia virus recombinants in which the upstream insertion of shotgun-isolated vaccinia genomic fragments of 156 to 379 bp promoted this expression. Two of these fragments were related in such a manner that 62 bp separated two divergent early transcription start sites. The region of imperfect dyad symmetry revealed in this fragment is proposed to result from the presence of two divergent early transcription signals of vaccinia virus. Subsequent comparison showed that domains with high sequence homologies to those depicted by the dyad symmetry existed at comparable locations in the sequences flanking both the HSV-TK mRNA start site of the other two recombinants and that of several early vaccinia genes. Maximum homologies among these conserved sequences was obtained when they were aligned discontinuously. These studies also revealed a late mRNA start site with no more than 10 bp of vaccinia sequences upstream.

Animals↗
PubMed1987

Modified methods for measuring citrulline and carbamoyl-beta-alanine with reduced light sensitivity and sucrose interference.

Two modified procedures for the colorimetric quantitation of citrulline aimed primarily at the assay of ornithine transcarbamylase were developed. Both methods give highly reproducible results in a short period of time since color is developed in 25 min at 100 degrees C. One method is more sensitive than previous methods and the other is as sensitive but requires less than one-fifth as much acid for color development. The reduction in acid concentration results in the stability of the colored complex for at least 50 min under the laboratory lighting conditions and allows for the presence of 5 mumol sucrose and 0.03 mumol mercaptoethanol in the assay. A low-acid modification for quantitating carbamoyl-beta-alanine is described also and may be applicable to the assay of dihydropyrimidinase.

Alanine↗
PubMed1985

Isolation of cis-acting vaccinia virus DNA fragments promoting the expression of herpes simplex virus thymidine kinase by recombinant viruses.

Recombinant TK- vaccinia viruses containing the pBR322 sequence inserted in either orientation within the coding sequence of the viral thymidine kinase gene were constructed. They were characterized by genomic analysis, hybridization studies, reversion to wild-type virus by in vivo recombination, and rescue from their genomes of plasmids which contained all or parts of the pBR322 sequence. TK- cells were infected with one of these recombinant viruses and then transfected with pools of chimeric plasmids composed of a cloned herpes simplex virus thymidine kinase gene which contained upstream inserts of different vaccinia DNA fragments prepared by restriction or sonication. Recombination between homologous pBR322 sequences within infected cells generated selectable recombinant viruses in which expression of the herpes simplex virus thymidine kinase gene was promoted by the upstream vaccinia insert. These viruses were characterized by genomic analysis, hybridization, and in vivo or in vitro phosphorylation of (5-[125I]deoxycytidine as a specific assay for the expressed herpes simplex virus thymidine kinase. Vaccinia DNA inserts were isolated conveniently for transfer to bacteria by rescuing appropriate plasmids from the genome of recombinant viruses. The sequence of 100 nucleotides adjacent to the upstream region of the herpes simplex virus gene was determined in nine different inserts measuring 0.17 to 1.07 kilobase pairs.

Base Sequence↗
PubMed1982

Expression of vaccinia virus early mRNA in Ehrlich ascites tumor cells. 1. Translation of cellular and viral early mRNA in cell-free systems from uninfected and virus-infected cells at the early stage.

Translation of cellular and early vaccinia RNA in nuclease-treated lysates, derived from uninfected and vaccinia-virus-infected cells at the early stage, has been investigated. When using limiting amounts of RNA no discrimination of translation was observed in the infected cells lysates; this conclusion was confirmed by sensitive RNA competition experiments for translation in vitro and also when using two different fractionated systems for protein synthesis in vitro. This absence of detectable discrimination in vitro was established both by comparing incorporation of [35S]methionine into proteins and by analysis of the products thus synthesized by sodium dodecylsulfate gel electrophoresis. However, a modification of the translational machinery from vaccinia-virus-infected cells did occur since the only the ribosomal salt wash derived from infected cells was able to reverse the inhibition of protein synthesis in vitro resulting from excess RNA (control or early). This property of vaccinia-virus-infected cell lysates may result from the synthesis l machinery from vaccinia-virus-infected cells did occur since the only the ribosomal salt wash derived from infected cells was able to reverse the inhibition of protein synthesis in vitro resulting from excess RNA (control or early). This property of vaccinia-virus-infected cell lysates may result from the synthesis l machinery from vaccinia-virus-infected cells did occur since the only the ribosomal salt wash derived from infected cells was able to reverse the inhibition of protein synthesis in vitro resulting from excess RNA (control or early). This property of vaccinia-virus-infected cell lysates may result from the synthesis of an early protein involved in translation or from a better recovery of translational factors from the infected cells, as suggested in the accompanying paper.

Animals↗