Drosophila melanogaster poly(A)-binding protein: cDNA cloning reveals an usually long 3′-untranslated region of the mRNA, also present in other eukaryotic species

Abstract Two classes of cDNAs encoding the Drosophila melanogaster poly(A)-binding protein (PABP), which differ in length due to different positions of their respective 3′ ends, were isolated by screening an embryonic cDNA library. These cDNAs hybridize to a single chromosomal site at position 55B on the right arm of the second chromosome. A unique 3.8-kb PABP mRNA species was detected, indicating that ‘long’ cDNAs correspond to full-length cDNAs and that the 3′-untranslated region of the D. melanogaster mRNA is close to 1.5 kb long. The PABP transcript accumulates in oocytes, is maternally inherited by the embryo and present at every developmental stage tested. The D. melanogaster PABP cDNAs contain a 1722-nt ORF encoding a 64-kDa protein. This protein contains four RNA-binding domains which show limited primary sequence divergence during evolution, in contrast to the C-terminal third of the protein. The strikingly long 3′-untranslated region of the D. melanogaster PABP mRNA is shown to exist also in other eukaryotes including vertebrate species. It suggests that important regulatory sequences intrinsic to the PABP mRNA are present within this 3′-untranslated region.