Molecular and genetic analysis of glucocorticoid-responsive mouse mammary tumor virus gene expression /
| Main Author: | |
|---|---|
| Other Authors: | , , |
| Format: | Thesis Book |
| Language: | English |
| Published: |
1988.
|
| Subjects: | |
| Online Access: | ProQuest, Abstract Link to OAKTrust copy |
| Abstract: | Three intact copies of endogenous mouse mammary tumor virus proviral DNA are present at distinct genetic loci Mtv-8, Mtv-9, and Mtv-17 in inbred C57BL/6 mice. The DNA sequence of transcriptional control regions of the LTRs of all three endogenous proviral units was determined; this analysis revealed multiple base differences in the defective LTR of Mtv-17 compared to the sequences of the functional LTRs from Mtv-8 and Mtv-9. Further studies of the effects of base differences on the transcriptional regulation of this LTR have attributed the transcriptional defect to a single G to A transition at position -75 with respect to the site of transcription intiation that resides within the previously defined binding site for the transcription factor nuclear factor 1. To study potential trans-acting factors required for the regulation of the MMTV LTR promoter, a genetic approach was designed to select variant cell lines with altered responsiveness to glucocorticoid hormones. The Escherichia coli xanthine-guanine phosphoribosyl transferase gene (Ecogpt) was used as the selectable marker and was linked to the glucocorticoid-responsive promoter of MMTV to form plasmid pMTVgpt. Several pMTVgpt+ transformants in which Ecogpt expression was induced by glucocorticoids were identified and served as parental cell lines for selection of variants. Mycophenolic acid was used to select variant cells which could constitutively express Ecogpt in. the absence of glucocorticoids, and 6-thioxanthine was used to select against expression of Ecogpt. Gene amplification of pMTVgpt DNA was observed in constitutive expression variants, but no gross changes of pMTVgpt DNA occur in the genome of 6-thioxanthine-resistant (6-TXr) variants. A cis/trans test was performed and the result suggests that transacting factor(s) might be involved in the altered glucocorticoid responsiveness of at least some variant cells. Analysis of glucocorticoid receptors from these variants and their respective parental lines revealed no significant differences with regard to molecular weight, binding affinity for hormone, binding affinity to DNA-cellulose, and dosage of the glucocorticoid receptor gene. However, the number of receptor binding sites for the glucocorticoid hormones is different between some of the 6-TXr variants and the parental clone... |
|---|---|
| Item Description: | Typescript (photocopy). Vita. "Major subject: Biochemistry." |
| Physical Description: | xi, 80 leaves : illustrations ; 29 cm |
| Bibliography: | Includes bibliographical references (leaves 68-79). |