We report the results of sequence analysis and chromosomal distribution of all distinguishable long terminal repeat (LTR) retrotransposons (Cer elements) in the Caenorhabditis elegans genome. Included in this analysis are all readily recognizable full-length and fragmented elements, as well as solo LTRs. Our results indicate that there are 19 families of Cer elements, some of which display significant subfamily structure. Cer elements can be clustered based on their tRNA primer binding sites (PBSs). These clusters are in concordance with our reverse transcriptase-and LTR-based phylogenies. Although we find that most Cer elements are located in the gene depauperate chromosome ends, some elements are located in or near putative genes and may contribute to gene structure and function. The results of RT-PCR analyses are consistent with this prediction.

Amphitrite ornata, a terebellid polychaete, inhabits marine environments that are contaminated by biogenically produced halometabolites. These halogenated organic compounds are toxic and quite diverse. To survive in this environment, A. ornata produces a novel dehaloperoxidase (DHP I) that detoxifies haloaromatic compounds. In this study we identified and characterized two dehaloperoxidase genes, designated dhpA and dhpB, from an A. ornata complementary DNA library. The deduced amino acid sequences (DHP A and DHP B) of the two dhp genes both contain 137 amino acid residues, but they differ at 5 amino acid positions. Allelic variation was observed for both genes as well. Polymerase chain reaction-restriction fragment length polymorphism assays of genomic DNA from 19 in individuals showed that each individual contains both the dhpA and the dhpB genes. Therefore, the two types of DHP are encoded by separate genes and are not alleles of a single gene. Furthermore, DHP A and DHP B may have different substrate specificities since they have amino acid differences in the active site.

Despite the global prevalence of marine sedimentary habitats, the potential for chemically mediated ecological interactions within these assemblages remains poorly known. Using GUMS, we examined methanol extracts of worm, mollusc, and crustacean macroinfauna from 2 local intertidal sandflat communities for volatile organohalogens, a common, often bioactive class of secondary metabolites from marine organisms. Halogenated compounds were newly identified from 11 common polychaete species in the farnil~es Capitellidae, Chaetopteridae, Cirratulidae, Glyceridae, Pectinarudae and Spionidae. Tentative structures of these halometabolites are proposed based on G U M S data. The represented chemical classes included aromatic mono-and dibrominated hydroxyphenylpropanoids, nitrogen-containing bromoalkylpyrroles, as well as brominated and chlorinated hydrocarbons and sulfides. Among the molluscs, only Terebra dislocata (Prosobranchia) contained an organohalogen compound (2,6-dibromophenol), which is likely derived from its diet of hemichordate worms. Volatile haloorganics were not found in amphipod and nemertean taxa. Possession of these compounds was not a function of any particular phylum, size categorization, or trophic mode, although hemichordates and all Capitellid and Spionid polychaetes collected at these sites invariably contained halocompounds. Most (40 of ca 54 taxa) of the numerically dominant macroinfaunal taxa at these 2 sites were examined in this survey; of these, 4 3 % contained halometabolites, including the broadly distributed species Mediomastus arnbiseta, Heteromastus filiformis, Streblospio benedicti, Thary.~ marioni, and Saccoglossus kowalevskii. Thus, the potential for widespread occurrence of halogenated compounds among infauna is great. The presence of organohalogens in many common and abundant polychaete species suggests a general biological significance for these metabolites, a result of potential interest to marine ecologists, toxicologists and environmental chemists.

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