An essential step in the replication cycle of all retroviruses is the dimerization of genomic RNA prior to or during budding and maturation of the viral particle. In HIV-1 a 5′ leader region site referred to as stem-loop1 (SL1) promotes RNA dimerization in vitro and influences dimerization in vivo. In HIV-2, two sequences promote dimerization of RNA fragments in vitro: the 5′-end of the primerbinding site (PBS) and a stem loop homologous to the HIV-1 SL1 sequence. Because HIV-2 RNA constructs of different lengths use these two dimerization signals disproportionately, we hypothesized that other sequences could modulate their relative utilization. Here, we characterized the influence of sequences upstream and downstream of the major splice donor site on the formation of HIV-2 RNA dimers in vitro using a variety of RNA constructs and dimerization/electrophoresis protocols. We first assayed the formation of loose or tight dimers for 1-444 and 1-561 model RNAs. Although both RNAs could form PBS-dependent loose dimers, the 1-561 RNA was unable to make SL1-dependent tight dimers. Using RNAs truncated at their 5′ and/or 3′ ends and by making compensatory base substitutions we found that two elements interfere with the formation of SL1-dependent tight dimers. The cores of these elements are located at nucleotides 189-196 and 543-550. Our results suggest that base pairing between these sequences prevents the formation of SL1- † This research was supported by the National Institutes of Health grant number AI45388 to J.S.L.

Water samples from Great South Bay, New York, contained biological agents capable of causing the lysis of the brown‐tide alga Aureococcus anophagefferens Hargraves et Sieburth. From these water samples, 32 bacterial isolates were tested for algicidal effects against the algae. Six of the isolates were shown to have algicidal effects against A. anophagefferens. Sequencing of the gene 16S rRNA revealed that the isolates were relatively diverse. Based on their similarity to sequences in repositories, the isolates seem to be closely related to Bacillus, Halomonas, Croceibacter atlanticus, Marinobacter, and an Arctic deep‐sea bacterium.