K. Sumiyama et al., CLASS-III POU GENES - GENERATION OF HOMOPOLYMERIC AMINO-ACID REPEATS UNDER GC PRESSURE IN MAMMALS, Journal of molecular evolution, 43(3), 1996, pp. 170-178
The class III POU transcription factor genes play an important role in
the nervous system. Comparison of their entire amino acid sequences d
isclosed a remarkable feature of particular mammalian class III POU ge
nes. Alanine, glycine, and proline repeats were present in the mammali
an Brain-1 gene, whereas most of these repeats were absent in the nonm
ammalian homologue. The mammalian Brain-2 gene had alanine, glycine, p
roline, and glutamine repeats, which were missing in the nonmammalian
homologue. The mammalian Scip gene had alanine, glycine, proline, and
histidine repeats, but the nonmammalian homologue completely lacked th
ese repeats. In contrast, the mammalian Brain-4 gene had no amino acid
repeats like its nonmammalian homologue. The mammalian genes containi
ng the characteristic amino acid repeats had another feature, higher G
C content. We found a positive correlation between the GC content and
the amino acid repeat ratio. Those amino acids were encoded by triplet
codons with relatively high GC content. These results suggest that th
e GC pressure has facilitated generation of the homopolymeric amino ac
id repeats.