Diversity of LTR retrotransposons and their role in genome reorganization
We have characterized the copia RNA in the cytoplasm of cultured Drosophila cells. Copia RNA was detected and purified by hybridization to DNA of the plasmid cDm 1142, which contains the copia sequence. A large fraction (2.2%) of the total cytoplasmic poly(A)+ RNA was found to be copia RNA. Cytoplasmic copia RNA displays all the characteristics expected for a messenger RNA. It possesses a poly(A) tract identical in length with that of total poly(A)+ cytoplasmic RNA. It is associated with polysomes and can be released from this association by treatment with EDTA. When purified copia RNA is added to an mRNA-dependent rabbit reticulocyte lysate, three polypeptides of 51000, 33000, and 21000 daltons are seen. We have not determined if these are different polypeptides or if the two smaller polypeptides are fragments of the 51000-dalton polypeptide. The half-life of copia cytoplasmic RNA was determined in pulse--chase experiments to be 9.5 h; this is 1.6 times longer than the half-life of the intermediate decay class of total poly(A)+ cytoplasmic RNA. These properties provide strong evidence that copia RNA functions in vivo as a messenger RNA.