Effect of a short term fast on the distribution of cytoplasmic albumin messenger ribonucleic acid in rat liver. Evidence for formation of free albumin messenger ribonucleoprotein particles.

Recently, using molecular hybridization techniques with albumin [3H]cDNA, we have determined that in normally fed rats 98% of total liver polyribosomal albumin mRNA sequences are found in membrane-bound polyribosomes (Yap, S. H., Strair, R. K., and Shafritz, D. A. (1977) Proc. Natl. Acad. Sci. U. S. A. 74, 5397-5401). We now observe that a 24- to 30-h withdrawal of food leads to major changes in the amount and subcellular distribution of albumin mRNA molecules. The total amount of cytoplasmic albumin mRNA per liver and concentration of albumin mRNA per unit of membrane-bound polyribosomal RNA are decreased. However, the proportion of albumin mRNA present in the postribosomal supernatant fraction increases dramatically in a short term fast, so that it now represent 60% of total cytoplasmic albumin mRNA sequences. Most of the albumin mRNA sequences in the postribosomal supernatant fraction sediment between 30 S and 50 S. These findings suggest that albumin mRNA is probably stored in the messenger ribonucleoprotein fraction during the fasting state.