A nuclear post-transcriptional event responsible for overproduction of argininosuccinate synthetase in a canavanine-resistant variant of a human epithelial cell line.
The Canr1 cell line, a canavanine-resistant variant of the cultured human epithelial cell line, RPMI 2650, overproduces argininosuccinate synthetase more than 200-fold. Run-on transcription assays showed no significant difference in transcription initiation of the argininosuccinate synthetase gene between Canr1 and RPMI 2650 cells. Furthermore, no difference in the relative transcription rate was seen along this 63-kb gene, suggesting that neither transcription initiation nor elongation is responsible for differential expression of argininosuccinate synthetase in these two cell lines. However, when isolated nuclei were labeled for a longer period of time in the transcription assay, precursor RNA of argininosuccinate synthetase in RPMI 2650 cells was found to be very labile. Apparently, a nuclear event affecting precursor RNA stability is responsible for the dramatic difference in argininosuccinate synthetase levels in these two cell lines. Using a microsatellite polymorphic marker, it was demonstrated that argininosuccinate synthetase from both alleles of the gene in Canr1 cells was overexpressed. This suggests that a trans-acting mechanism may be responsible for regulation of overproduction in this cell line. Furthermore, when protein synthesis was blocked by cycloheximide, less precursor RNA was observed in Canr1 cells. These data suggest that a labile protein factor(s) participates in the regulation.
Tsai
T F
TF
Graduate Institute of Microbiology and Immunology, National Yang-Ming University, Taiwan, Republic of China.
Su
T S
TS
D001124:Argininosuccinate Synthase / Q000096:biosynthesis*; D001483:Base Sequence; D002172:Canavanine / Q000494:pharmacology*; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D018076:DNA, Complementary; D004351:Drug Resistance; D004848:Epithelium / Q000201:enzymology; D006801:Humans; D008969:Molecular Sequence Data; D012313:RNA / Q000032:analysis; D012323:RNA Processing, Post-Transcriptional
D018076:DNA, Complementary; D002172:Canavanine; D012313:RNA; D001124:Argininosuccinate Synthase