Presence of albumin mRNA precursors in nuclei of analbuminemic rat liver lacking cytoplasmic albumin mRNA.

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Abstract
Analbuminemic rats, which lack serum albumin, were previously found to have no albumin mRNA in the cytoplasm of the liver. The existence of nuclear albumin mRNA precursors in the liver of analbuminemic rats was examined by RNA cDNA [complementary DNA] hybridization kinetics. Albumin mRNA precursors were present in the nuclei of analbuminemic rat liver at almost normal levels, despite the absence of albumin mRNA from the cytoplasm. Nuclear RNA of analbuminemic rat liver was subjected to electrophoresis on 1% agarose gel in parallel with nuclear RNA of normal rat liver. RNA was transferred from the gel to diazobenzyloxymethyl-paper and hybridized to cloned cDNA. Several bands of putative albumin mRNA precursors were obtained with nuclear RNA of analbuminemic rat liver and some of them were indistinguishable from those of normal rat liver. Nuclear RNA of analbuminemic rats was hybridized to 3''-end-labeled cloned cDNA under the condition of RNA excess and then digested completely with SI nuclease and subjected to electrophoresis on polyacrylamide gel. By this technique, nuclear RNA that could hybridize to cDNA was found to have the albumin mRNA sequence in at least the 3'' half of the mRNA that was covered by cloned cDNA. For comparison of the structure of the albumin genes of analbuminemic and normal rats, DNA from rat livers of both types were digested completely with EcoRI, HindIII and Pst I; the fragments were separated by electrophoresis on 1% agarose gel, transferred to nitrocellulose paper and hybridized to clone cDNA. The intensities of the corresponding bands and the digestion patterns of the analbuminemic and normal rat genes were indistinguishable. Analbuminemic rats have a unique type of mutation(s) affecting albumin mRNA maturation.