Brain-specific promoter and polyadenylation sites of the  -adducin pre-mRNA generate an unusually long 3'-UTR

Adducins are a family of membrane skeleton proteins composed of alpha-, beta- and gamma-subunits that promote actin and spectrin association in erythrocytes. The alpha- and gamma-subunits are expressed ubiquitously, while the beta-subunit is found in brain and erythropoietic tissues. The brain beta-adducin protein is similar in size to that of spleen, but the mRNA transcript is a brain-specific one that has not been yet characterized, having an estimated length of 8-9 kb instead of the 3-4 kb of spleen mRNA. Here, we show the molecular basis for these differences by determining the structure of the brain-specific beta-adducin transcript in rats, mice and humans. We identified a brain-specific promoter in rodents that, apparently, was not conserved in humans. In addition, we present evidence that the brain-mRNAs are formed by a common mechanism consisting in the tissue-specific use of alternative polyadenylation sites generating unusually long 3'-untranslated region of up to 6.6 kb. This hypothesis is supported by the presence of highly-conserved regions flanking the brain-specific polyadenylation site that suggest the involvement of these sequences in the translational regulation, stability and/or subcellular localization of the beta-adducin transcript in the brain.