RHODOPSINS FROM 3 FROG AND TOAD SPECIES - SEQUENCES AND FUNCTIONAL COMPARISONS

The frequency of thermal 'dark events' in the membrane current of rhod opsin rods of the bullfrog, Rana catesbeiana, is considerably lower th an observed in rods of two toad species, even though all three rhodops ins have approximately the same absorbance characteristics. In order t o map amino acid substitutions possibly associated with thermal stabil ity in the genus Rana, the cDNA's coding for the rhodopsins of Bufo bu fo, B. marinus and R. temporaria were sequenced and the conceptually t ranslated protein sequences aligned to the previously sequenced rhodop sins of R. catesbeiana, R. pipiens and Xenopus laevis. Across the six anuran species studied, there are sixteen non-conserved substitutions and six changes that include gain or loss of a hydroxyl group. Serine or threonine at position 220 is unique to the three Rana species, phen ylalanine at position 270 is unique to all three Ranas and to X. laevi s, and phenylalanine at position 274 is unique to both species of the genus Bufo. This investigation produces a list of substitutions that a re candidates for future studies of thermal stability. Ln addition, a number of amino acids are identified that apparently do not influence absorbance characteristics, at least not cumulatively, (C) 1998 Academ ic Press Limited.