Analysis of fusion gene and encoded photopigment of colour-blind humans.
In humans, long-wavelength-sensitive and middle-wavelength-sensitive cone pigments are encoded by genes lying in a head-to-tail tandem array on the X chromosome. Deficiencies in red-green colour vision seem to arise from unequal recombination of these normal X-linked genes. In some dichromats this recombination is believed to yield a fusion gene encoding a product with an absorption spectrum similar to that of one or the other of the normal photopigments. Until now, however, such a relationship between the structure of a pigment gene and the spectral properties of its encoded pigment has not been directly shown. We have now sequenced a fusion gene isolated from a red-green colour-blind human and determined the spectral properties of the pigment that it encodes. The absorption spectrum of the photopigment was very similar to that of normal middle-wavelength-sensitive photopigment, even though about half of its DNA coding sequence seems to be derived from a gene encoding normal long-wavelength-sensitive pigment. These results indicate the regions of the X-encoded photopigment apoproteins that are responsible for differences in their spectral tuning, and imply that the striking variations in colour vision among anomalous trichromats of a particular type are not attributable to anomalous pigments with differing spectral peaks.
Neitz
J
J
Department of Psychology, University of California, Santa Barbara 93106.
Neitz
M
M
Jacobs
G H
GH
D000328:Adult; D000595:Amino Acid Sequence; D001483:Base Sequence; D003117:Color Vision Defects / Q000235:genetics*; D004247:DNA / Q000235:genetics; D004596:Electroretinography; D005091:Exons; D006801:Humans; D008297:Male; D008969:Molecular Sequence Data; D009693:Nucleic Acid Hybridization; D010786:Photoreceptor Cells / Q000378:metabolism; D012150:Polymorphism, Restriction Fragment Length; D011995:Recombination, Genetic / Q000235:genetics*; D015183:Restriction Mapping; D012168:Retinal Pigments / Q000235:genetics*; D013053:Spectrophotometry; D014960:X Chromosome
D012168:Retinal Pigments; D004247:DNA