Molecular Cloning and Characterization of the Hamster Preproenkephalin A cDNA

The cDNA for hamster preproenkephalin A (ENK) was cloned from an adrenal gland cDNA library constructed in the λ ZapII vector. A nearly full-length cDNA was obtained and its 5′ end region was completed using the technique of rapid amplification of cDNA ends (RACE). The coding and 3′ untranslated regions of the hamster ENK cDNA share a high sequence identity with the rat, human, and bovine cDNAs, whereas the sequence identity is lower for the 5′ untranslated region. Southern blot analysis of genomic DNA digests showed that a single copy of the ENK gene is present in the hamster haploid genome. Northern blot analysis of poly(A)⁺RNA from various hamster tissues indicated the following rank order for ENK messenger RNA abundance: adrenal glands > right atrium > brain > left atrium > right ventricle > ventricular septum > left ventricle, whereas primer extension analysis showed a single, identical transcriptional initiation site for the ENK mRNA in all these tissues. The sequence of the 5′ untranslated region of the heart ENK cDNA was found to be identical to that from adrenal glands. This rules out the possibility that structural divergences in the 5′ untranslated region of the heart ENK mRNA could decrease its translation efficiency and contribute to the very low level of enkephalin-containing peptides in the heart, compared to the adrenal glands.