RNA synthesis and number of transcribing polymerase molecules in ischemic liver nuclei

Rat alpha 1-fetoprotein messenger RNA: 5'-end sequence and glucocorticoid-suppressed liver transcription in an improved nuclear run-off assay

Cloned cDNA fragments spanning nearly the entire coding regions of rat AFP and albumin genes were used in liver nuclear run-off assays. Under standard assay conditions, transcription signals detected with 5' probes were systematically stronger than with 3' probes. Heparin eliminated this phenomenon, which suggests that nuclear run-off assays are subject to in vitro reinitiation occurring preferentially in promoter gene regions. Transcription in the presence of heparin indicates that very few polymerases are engaged on the AFP gene in adult rat liver. Dexamethasone treatment of developing rat liver results in the loss of transcribing polymerases from all regions of the AFP gene. Albumin gene transcription is unaffected. Inhibition of liver protein synthesis with cycloheximide does not modify the AFP gene suppressive action of dexamethasone. Glucocorticoid hormone receptors may thus directly interact with the AFP locus, blocking polymerase initiation. We also report the sequence analysis of rat AFP mRNA, which reveals the existence of two potential initiation codons on this molecule.

Mechanism of enhanced RNA synthesis in acute-phase rat liver and its relationship to chromatin structure

Nuclei isolated from the liver of rats undergoing an acute inflammatory reaction induced by turpentine treatment show increased RNA synthesis. This increase is essentially determined by a faster polyribonucleotide-elongation rate while the number of transcribing polymerase molecules is unchanged. The sensitivity of chromatin to micrococcal-nuclease digestion and the composition of chromosomal proteins are not affected by the acute-phase process. Therefore the increased RNA synthesis by liver nuclei from acutely inflamed rats does not seem to correlate with major changes in chromatin structure.