α-fetoprotein and Albumin Genes of Rats: No Evidence for Amplification-Deletion or Rearrangement in Rat Liver Carcinogenesis

Abstract

Full-length radiolabeled albumin and alpha --fetoprotein (AFP) cDNAs were synthesized from pure albumin and AFP mRNA preparations by using avian myeloblastosis virus reverse transcriptase (RNA-dependent DNA polymerase). The cDNAs have been used to quantitate the number of albumin and AFP genes in different rat tissues by two independent methods, both of which yielded similar results. First, the kinetics of the association of these cDNAs with nuclear DNA from rat liver, rat kidney, and Morris hepatoma 7777 under conditions of vast DNA excess indicated that the albumin and AFP mRNAs are transcribed from ``nonrepetitive DNA.'' Second, saturation hybridization experiments in which a constant amount of rat liver DNA or Morris hepatoma 7777 was hybridized with increasing amounts of cDNA to albumin mRNA have shown the presence of 1-2 albumin genes per rat haploid genome. The number of AFP genes obtained in similar titration experiments was approximately 2-3. This was true whether rat liver DNA or hepatoma 7777 DNA was used in the reassociation experiments. When high molecular weight DNA preparations from both these tissues were digested with the restriction endonuclease EcoRI and the fragments were transferred to a nitrocellulose filter, the albumin and AFP [32P]cDNA probes hybridized to different sets of DNA fragments. However, each probe gave the same hybridization pattern whether Buffalo rat liver DNA or hepatoma 7777 DNA was utilized.