Expression of asparagine independence in variants of ICR 2A haploid frog cells.
J Cell Physiol
; 139(1): 175-80, 1989 Apr.
Article
em En
| MEDLINE
| ID: mdl-2565340
ABSTRACT
Properties of the change from asparagine dependence (asn-) to independence (asn+) were investigated in the androgenetic haploid frog cell line ICR 2A. Two types of asn+ variants arose spontaneously during culture. Glutamine-dependent asparagine synthetase (AS) activity, found to be deficient in asn- cells, was repressed by asparagine in one type of variant and expressed constitutively in the other. No quantitative differences in AS-specific DNA sequences or changes in ploidy were evident between asn+ and asn- cells. The asn+ frequency in ICR 2A populations, not dramatically influenced by chemical mutagens, was increased 130-fold by exposure to 5-azacytidine. The methylation of CCGG sequences at the 5' end of the AS structural gene was found to be reduced equally in both types of asn+ variant. These results indicate that decreased DNA methylation is essential but not necessarily sufficient for the expression of AS activity in this frog cell system.
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Base de dados:
MEDLINE
Assunto principal:
Asparagina
/
Variação Genética
/
Haploidia
Limite:
Animals
Idioma:
En
Ano de publicação:
1989
Tipo de documento:
Article