The largest group of transposable elements in Drosophila melanogaster, copia-like elements, share some important structural features with and are intimately related in evolution to vertebrate retroviruses. To further clarify the relationship between retroviruses and copia-like transposable elements, we set out to determine the complete nucleotide sequence of the genome of 17.6, which has long terminal repeats homologous in nucleotide sequence to those of avian leukaemia-sarcoma virus. We report here that 17.6 contains three long open reading frames comparable with gag, pol and env genes in retrovirus. At the level of amino acid sequence, the longest open reading frame of 17.6 includes a coding sequence similar to that for reverse transcriptase, suggesting a role for this enzyme in the life cycle of some Drosophila copia-like elements, analogous to the situation in retrovirus.

We have made a computer-assisted search for homology among polymerases or putative polymerases of various viruses and a transposable element, the Drosophila copia-like element 17.6. The search revealed that the putative polymerase (second open reading frame) of the copia-like element 17.6 bears close resemblance in overall structural organization to the pol gene product of Moloney murine leukaemia virus (M-MuLV): they show significant homology to each other at both the Nand C-terminal portions, suggesting that the 17.6 putative polymerase carries two enzymatic activities, related to reverse transcriptase and DNA endonuclease. The putative polymerase of cauliflower mosaic virus (CaMV) shows striking homology with the putative polymerase of 17.6 over almost its entire length, but it lacks the DNA endonuclease-related sequence. Furthermore, it was shown that the N-terminal ends of the M-MuLV pol product and the CaMV and 17.6 putative polymerases exhibit strong sequence homology with the gag-specific protease (p15) of Rous sarcoma virus (RSV) as well as the amino acid sequence predicted from the gag/pol spacer sequence of human adult T-celi leukaemia virus (HTLV). These p15-related sequences contain a highly conserved stretch of amino acids which show a close similarity with sequences around the active site amino acids Asp-ThrGly of the acid protease family, suggesting that they have an activity similar to acid protease. On the basis of the alignment of reverse transcriptase-related sequences, a dendrogram representing phylogenetic relationships among all the viruses compared together with 17.6 was constructed and its evolutionary implication is discussed.

We have shown previously that Drosophila cells contain virus-like particles (VLPs) containing 5-kilobase (kb) RNA that hybridizes to a transposable element, termed copia. We have suggested that VLPs and copia are derivatives of viral particles and proviral forms, respectively, of 'copia' retrovirus, a putative Drosophila retrovirus. To further clarify the relationship between copia and copia-related RNA in VLPs (VLP H-RNA), we determined and compared their nucleotide sequences. VLP H-RNA was found to be an unspliced, genome-sized transcript of copia, and, like retroviral genome RNA, VLP H-RNA is terminally redundant with termini localized in the long terminal repeats (LTRs) of copia. VLP H-RNA contains two long open reading frames (ORFs), one of which includes the coding sequence for a predominant VLP protein of relative molecular mass (Mr) 31,000 (31K). Here we show that, in contrast to 17.6 ORF2, ORFs of copia have no extensive amino-acid sequence homology to the RT region of the reverse transcriptase of retrovirus in vertebrates. Because of a one-base insertion/deletion, the two ORFs in VLP H-RNA are fused and become a single, longer ORF in a genomic copia.

The nucleotide sequence of the internal region of a Drosophila retrotransposon. 412, was determined. The genome of 412 was found to consist of two long open-reading frames (ORFs 1 and 2), an unusually long putative leader region and long terminal repeats (LTRs). As with 17.6, 297 and gypsy, ORFs 1 and 2 slightly overlap each other and are out of phase by + 2 . ORF2 includes the nucleotide sequences coding for the putative protease, reverse transcriptase and integrase, and is similar in entire organization to the pol gene of Moloney murine leukaemia virus. In spite of the difference in insertion specificity, integrase, an enzyme presumably responsible for insertion, was found to be similar in amino acid sequence to the counterparts of 17.6, 297 and gypsy. There is no ORF in 412 which corresponds to retroviral env or ORF3s of 17.6 and 297. Analysis of 412 transcripts suggested that 412 LTR is composed of U3, R and U5. The gene for a potential primer tRNA for putative reverse transcription of 412 was also surveyed and the 3'-terminal 15 nucleotides of a putative arginine tRNA were found to be exactly complementary to the putative primer-binding site of 412.Drosophila copia-like elements or retrotransposons are formed from the largest group of transposable genetic elements in Drosophila melanogaster. They are intimately related in evolution to retroviral proviruses in vertebrates In our previous experiments the complete nucleotide sequences of three Drosophila retrotransposons 17.6 [15], 297 [16] and copia [17] were determined. 17.6 and 297 contained three open reading frames (ORFs) similar in size and location to retroviral gag, pol and env. The second ORFs of these two elements were further shown each to include the nucleotide sequence coding for a reverse-transcriptase-like enzyme and be, in all respects of their organization, very similar to the pol gene of Moloney murine leukaemia virus (Mo-MuLV) [15,16, 181. In contrast, the genome of copia contained a single long ORF [17, 191 including genes for the major capsid protein of copia-related virus-like particles and reverse-transcriptase-like enzyme much less similar to the reverse transcriptase of MoMuLV [17,19]. These results suggest the genome organization in Drosophila retrotransposons to be very much diversified.To confirm and determine the further implications of this notion, a determination was made of the complete nucleotide sequence of another Drosophila retrotransposon, 412, having terminal dinucleotides identical to those of copia and retrovirus proviruses but different from those of 17.6, 297 and gypsy [4, 15-17, 20, 211. The genome of 412 was found to contain two long ORFs (ORFs 1 and 2) and an unusually long putative leader region with two short ORFs. As with 17.6 [15], 297 [16] and gypsy (unpublished), ORFs 3 and 2 slightly overlap each other and are out of phase by t 2 . The entire structure of ORF2 is of the 17.6 type and the putative integrase encoded by a portion of ORF2 is similar in amino acid sequence to the counterparts of 17.6, 297 and gy...

Several aromatic sesquiterpenoids displaying antifungal properties have been isolated from the liverwort Herberta adunca together with a mother hydrocarbon with a novel irregular sesquiterpene skeleton, entherbertane, and their structures and absolute configurations have been determined on the basis of extensive degradation reactions and spectroscopic evidence. The biological activity is also described. ' B. cinerea R. solani P. debaryanum * B. cinerea R. solani P. debaryanum * B . cinerea R. solani ~ P. debaryanum Concentration (p.p.m.)