The thermal stabilities of RNA:DNA hybrids are substantially greater than those of DNA:DNA duplexes in aqueous electrolyte solutions containing high concentrations of formamide. Association rates to form DNA:DNA duplexes and DNA:RNA hybrids have been measured in these solvents. There is a temperature range in which DNA:DNA rates are negligible and RNA:DNA rates close to optimal.

Green turtle fibropapillomatosis is a neoplastic disease of increasingly significant threat to the survivability of this species. Degenerate PCR primers that target highly conserved regions of genes encoding herpesvirus DNA polymerases were used to amplify a DNA sequence from fibropapillomas and fibromas from Hawaiian and Florida green turtles. All of the tumors tested (n = 23) were found to harbor viral DNA, whereas no viral DNA was detected in skin biopsies from tumor-negative turtles. The tissue distribution of the green turtle herpesvirus appears to be generally limited to tumors where viral DNA was found to accumulate at approximately two to five copies per cell and is occasionally detected, only by PCR, in some tissues normally associated with tumor development. In addition, herpesviral DNA was detected in fibropapillomas from two loggerhead and four olive ridley turtles. Nucleotide sequencing of a 483-bp fragment of the turtle herpesvirus DNA polymerase gene determined that the Florida green turtle and loggerhead turtle sequences are identical and differ from the Hawaiian green turtle sequence by five nucleotide changes, which results in two amino acid substitutions. The olive ridley sequence differs from the Florida and Hawaiian green turtle sequences by 15 and 16 nucleotide changes, respectively, resulting in four amino acid substitutions, three of which are unique to the olive ridley sequence. Our data suggest that these closely related turtle herpesviruses are intimately involved in the genesis of fibropapillomatosis.

play an important role in regulating the LTP. Increasing the proximity of PKC to its persistence ofthe enhanced response but not membrane-bound substrates could result in its amplitude. Since protein F1 appears to be the persistent elevation of substrate phosidentical to axonal growth-associated pro-phorylation, as has been observed with proteins and pp 46 (14)] and B-tein Fl phosphorylation 1 hour after LTP 50, which is related to PI turnover (15), its (18). Consistent with this scenario is the direct relation to synaptic enhancement (3, recent observation (19) that iontophoretic 5) may require such mechanisms, particular-application of phorbol ester, known to assoly presynaptic growth (16).ciate PKC with membranes (10, 11), enThe present results suggest a new mecha-hances the persistence of long-term synaptic nism for the long-term regulation of synap-plasticity in the dentate gyrus after LTP tic plasticity. Akers and A. Routtenberg, ibid. 334, I47 (198$). 7. R. B. Nelson and A. Routtenberg, Exp. Neurol. 89, 213 (1985