When dN/ dS is less than 1, there is evidence that purifying selection has been a predominant force during evolution, acting to remove changes in amino acid sequence and maintain protein function.
A low sequence homology can indicate that initial substitutions of amino acids had to be compensated for by secondary mutations to maintain protein function, resulting in constant conformational characteristics despite low sequence homology [ 27, 28].
All sequences started with ATG, and to maintain protein length, stop codons, when generated, were replaced by other random codons.
Under this model, the estimate of ω was 0.19, indicating that NAT1 sequences have been subject to strong purifying selection to maintain protein function over time.
We extracted the sequences from these putative homologous regions and conducted a gene prediction using GENSCAN [ 18] to identify whether these homologous sequences maintain protein-coding potential.
ShRNA resistant (shr) wt- and CCSS- LIMK1-myc were generated by mutating the shRNA target region while maintaining protein-coding sequence.
Likewise, nuclear export machinery is required to maintain proteins containing nuclear export signal (NES) sequences in the cytoplasm [18], [19].
This result is in accordance to Thorterson et al. [ 22], which established that the nucleotide diversity of ATM in the coding and non coding region have a ratio of 1 7.5, probably due to selective pressure for maintaining the protein sequence.
In all 15 cases, ω was less than 1 consistent with purifying selection acting to maintain the protein sequences.
It seems possible from our analysis that the high level of conservation of this gene may be necessary to maintain the protein sequences of both GPR27 and the matreshka.
