PROTEIN RESTRICTION SPECIFICALLY DECREASES THE ABUNDANCE OF SERUM-ALBUMIN AND TRANSTHYRETIN NUCLEAR TRANSCRIPTS IN RAT-LIVER

The expression of the genes for serum albumin and several other plasma proteins is decreased in animals consuming inadequate amounts of diet ary protein. To define the specificity of this phenomenon, we examined the effect of dietary protein restriction on the abundance of the mRN A for nine genes in rat liver. The results of this and previous studie s indicate that genes in liver can be divided into two classes based o n their response to protein restriction. Group I genes (albumin, trans thyretin, carbamyl phosphate synthetase-I, class I alcohol dehydrogena se, insulin-like growth factor-I) exhibit decreased expression in resp onse to protein restriction. In contrast, the expression of group II g enes (hypoxanthine-guanine phosphoribosyl transferase, ubiquitin, H-fe rritin, insulin like growth factor binding proteins-1, -2 and -4) is e ither unchanged or increased in response to protein restriction. To in vestigate the molecular mechanism(s) leading to the decreased level of albumin and transthyretin mRNA in protein-restricted animals, the eff ect of protein restriction on the abundance of albumin and transthyret in nuclear transcripts was examined. The results demonstrated that pro tein restriction specifically decreased the abundance of albumin and t ransthyretin nuclear transcripts, indicating that the reduction in mRN A levels is caused at least partly by a decrease in gene transcription .