Studies on the posttranscriptional site of cAMP action in the regulation of the synthesis of tyrosine aminotransferase.

Synthesis of L-tyrosine:2-oxoglutarate aminotransferase (EC 2.6.1.5) can be induced by N6,O2'-dibutyryl-adenosine 3',5'-monophosphate (Bt2cAMP) in Reuber H35 cell cultures. Actinomycin D fails to block this induction which indicates a target for Bt2cAMP at a posttranscriptional level. We have determined the influence of Bt2cAMP on several translational events during the tyrosine aminotransferase synthesis with the following results. (1) The number of nascent tyrosine aminotransferase chains increased, whereas no effect was measured on the number of nascent total protein chains. (2) The rate of elongation along the tyrosine aminotransferase mRNA and total mRNA is not enhanced by Bt2cAMP. (3) The induced synthesis of tyrosine aminotransferase is more sensitive to the inhibition of elongation. We conclude from our results that Bt2cAMP induces the synthesis of tyrosine aminotransferase by an increase in the rate of initiation on the tyrosine aminotransferase mRNA.