The visual pigment from the ultraviolet (UV) cone photoreceptor
of the tiger salamander has been cloned, expressed, and
characterized. The cDNA contains a full-length open reading
frame encoding 347 amino acids. The phylogenetic analysis indicates
that the highest sequence homology is to the visual pigments
in the S group. The UV opsin was tagged at the carboxy-terminus
with the sequence for the 1D4 epitope. This fusion opsin was
expressed in COS-1 cells, regenerated with 11-cis retinal
(A1) and immuno-purified, yielding a pigment with an absorbance
maximum (λmax) of 356 nm which is blue shifted
from the absorption of retinal itself. The transducin activation
assay demonstrated that this pigment is able to activate rod
transducin in a light-dependent manner. Regeneration with
11-cis 3,4-dehydroretinal (A2) yielded a pigment with
a λmax of 360 nm, only 4 nm red shifted from
that of the A1 pigment, while bovine rhodopsin generated
with A2 showed a 16-nm red shift from the corresponding A1 pigment.
These results demonstrate that the trend for a shorter wavelength
pigment to have a smaller shift of λmax between
the A1 and A2 pigments also fits UV pigments. We hypothesize
that the small red shift with A2 could be due to a twist in
the chromophore that essentially isolates the ring double bond(s)
from conjugation with the rest of the polyene chain.