Biomedical subjects

A E Simon

Publications and source records attributed to A E Simon.

60 records · Page 4Linked to original sources

PubMed1983

High-frequency mutation at the adenine phosphoribosyltransferase locus in Chinese hamster ovary cells due to deletion of the gene.

Evidence for a two-step model to explain the high-frequency expression of the recessive phenotype at the autosomal adenine phosphoribosyltransferase (APRT; EC 2.4.2.7) locus in Chinese hamster ovary (CHO) cells was given by Simon et al. [Simon, A. E., Taylor, M. W., Bradley, W. E. C. & Thompson, L. (1982) Mol. Cell. Biol. 2, 1126-1133]. This model proposed a high-frequency event, leading to allelic inactivation or a loss of gene function, and a low-frequency event, causing a structural alteration of the APRT protein. Either event could occur first, resulting in two classes of heterozygotes. We have analyzed the low-frequency event that gave rise to the class 2 aprt heterozygote D416 and the high-frequency event that led to APRT- cells derived from D416. Genomic Southern blots of Msp I- or Hpa II-digested DNA from wild-type CHO, aprt heterozygote D416, and two APRT- cell lines derived from D416 indicate a loss of a specific Msp I/Hpa II recognition sequence at one aprt locus in the heterozygote that correlates with the production of the electrophoretically altered APRT protein found in D416. The APRT- mutants are homozygous for the loss of this Msp I/Hpa II site. By using an additional CHO gene as an internal control, it was determined that the APRT- mutants contain only a single copy of the altered aprt gene. Thus, the high-frequency event that produces APRT- mutants derived from D416 is not an inactivation event but rather a deletion of the wild-type aprt gene.

Adenine Phosphoribosyltransferase↗

PubMed1983

Mechanism of mutation at the aprt locus in Chinese hamster ovary cells: analysis of heterozygotes and hemizygotes.

A two-step model to explain the high frequency of mutation at the diploid adenine phosphoribosyltransferase (aprt) locus in CHO cells has been proposed previously (Simon et al., Mol. Cell. Biol. 2:1126-1133, 1982). This model indicates that two distinct classes of aprt heterozygotes can be isolated. Class 1 heterozygotes, the most abundant class, were defined as those which arose spontaneously and were capable of undergoing mutation to the APRT- phenotype only at a low frequency (putative point mutation). Class 2 heterozygotes arose from a mutation and gave rise at a high frequency to APRT- cells. This high-frequency event has been identified as a deletion of the wild-type allele (A. E. Simon and M. W. Taylor, Proc. Natl. Acad. Sci. U.S.A. 80:810-814, 1983). In this paper we report further analysis of class 1 heterozygotes with respect to genetic structure, gene products, and karyotype. Our study indicated that class 1 heterozygotes contain two different types of mutants. About half have only one copy of the aprt gene and an unaltered karyotype, indicating that a deletion (similar to the high-frequency second-step event observed for class 2 heterozygotes) rather than a loss of the chromosome was responsible for the generation of the aprt+/- genotype. The remainder of the previously designated class 1 heterozygotes still contained two copies of the aprt gene (within the limits of the quantitation technique used) and arose presumably by a point mutation. One of this group, D423, was characterized with respect to aprt gene products and found to produce an electrophoretic variant in addition to the wild-type protein. APRT- mutants derived from D423 retained the same number of aprt gene copies as D423 and still synthesized a protein that comigrated with wild type, unlike APRT- mutants derived from class 2 heterozygotes. D423 and the other heterozygotes with two aprt genes therefore did not fit into either class 1 or 2 and are now designated class 3. The model we present suggests that only one of the two aprt alleles present in wild-type cells can undergo the deletion.

2-Aminopurine↗

PubMed1983

cDNA clones for Brassica napus seed storage proteins: evidence from nucleotide sequence analysis that both subunits of napin are cleaved from a precursor polypeptide.

Napins are a family of small, basic storage proteins synthesized in Brassica napus (rapeseed) embryos during seed maturation. Cultured embryos also synthesize napins but require exogenous abscisic acid (ABA) to maintain high accumulation rates. We synthesized cDNA from total RNA of embryos cultured on a medium containing ABA, and cloned it into the Pst1 site of pBR322. Two clones containing napin cDNA sequences selected by differential colony hybridization using [32P]cDNA probes from embryos grown with or without ABA were analyzed. These clones, pN1 (insert size = 583 bp) and pN2 (insert size = 739 bp), contained cDNA from two different napin mRNAs. The mRNAs to which they hybridized were found to encode a 21,000-dalton polypeptide that was immunoprecipitated by antibodies to mature napin (subunits of 9,000 and 4,000 daltons). The cDNA clones hybridized to an 850-base mRNA. Nucleotide sequencing demonstrated 95% homology between pN1 and pN2 cDNA inserts and predicted a precursor polypeptide of 178 amino acids, consistent with the 21,000 dalton in vitro translation product. Comparison of the deduced amino acid sequence with published amino acid compositions of mature napin subunits suggests that both the large and the small subunits are present in one precursor polypeptide, and that other regions of the precursor are removed during processing.

Amino Acid Sequence↗

PubMed1982

Model involving gene inactivation in the generation of autosomal recessive mutants in mammalian cells in culture.

We present evidence for a two-step model for expression of the recessive phenotype at the diploid adenine phosphoribosyl transferase (aprt) locus in Chinese hamster ovary cells. This model proposes a high-frequency event leading to allelic inactivation and a low-frequency event leading to a structural alteration of the APRT protein. Either event can occur first, resulting in two types of heterozygous cells. The proposed model is based on analysis of Chinese hamster ovary presumptive aprt heterozygotes and APRT- mutants, derived by two different laboratories. The major class of heterozygotes (class 1) had approximately 50% parental APRT activity, 50% immunologically precipitable APRT protein, and only wild-type enzyme as based on two-dimensional gel electrophoresis and thermal inactivation studies. We propose that one allele at the aprt locus has been inactivated in these heterozygotes. APRT- mutants derived from any single class 1 heterozygote arose at a low frequency and contained either no immunologically detectable APRT protein or an APRT enzyme which was, in most cases, demonstrably altered. The second class of heterozygotes, consisting of two independent isolates, gave rise to APRT- cells at a high frequency (10(-3) to 10(-5). These heterozygous cell lines had 50% of parental APRT activity and only wild-type spot, or wild-type and an electrophoretic variant spot, on two-dimensional gels. These aprt heterozygotes appear to have arisen by mutation at one allele. APRT- mutants derived from either heterozygote of this class had all lost the wild-type activity, consistent with the proposed model.

Adenine Phosphoribosyltransferase↗

PubMedDate not supplied

Prodromes of first-episode psychosis: how can we challenge nonspecificity?

Prevention of functional psychosis is a major concern of modern psychiatry. The aim is to avoid biological and psychosocial deterioration at the earliest possible stage of the illness. The term "prodrome" has become crucial for identification of the very early stage. Recent years have yielded intensive research effort in defining prodromal signs and symptoms; however, the conclusion of most researchers is that they are nonspecific. We present the descriptive and phenomenological findings of the prodrome concept. Although prodromes are nonspecific, their discrepancy with persisting social impairment over time is a frequently encountered and highly alarming feature in young at-risk individuals. The inclusion of phenomenological findings may suggest the presence of psychosis-like inner experiences already as early as the prodromal phase, and thus bears in itself the question of the starting point for psychopharmacological and psychosocial treatment. Finally, a decision pathway for clinicians is proposed in their difficult task of identifying young individuals at risk.

Adolescent↗

PubMedDate not supplied

Open reading frames of turnip crinkle virus involved in satellite symptom expression and incompatibility with Arabidopsis thaliana ecotype Dijon.

Carmoviruses are single-stranded, single component RNA viruses that include turnip crinkle virus (TCV) and the recently discovered cardamine chlorotic fleck virus (CCFV). Full-length, biologically active cDNAs were constructed for the TCV-M isolate and the Blue Lake isolate of CCFV. Using chimeric viruses constructed between isolates of TCV that produce mild or severe symptoms when coinoculated with a virulent satellite RNA, a Glu residue at position 1,144 in the polymerase open reading frame was identified as being involved in satellite-mediated symptom expression. To analyze viral determinants involved in resistance, chimeric viruses with precisely exchanged open reading frames were produced between TCV, which does not infect the Arabidopsis thaliana ecotype Dijon (Di-0), and CCFV, which can infect Di-0, TCV with the coat protein of CCFV was able to systemically infect Di-0 although whole plant hybridizations revealed that the hybrid virus spread more slowly than either of the two parental viruses. These results indicate that the two parental viruses. These results indicate that the coat protein is an important viral determinant in the resistance of Di-0 to TCV.

Amino Acid Sequence↗