Pachysolen tannophilusTOM JEFFERIESWhen recombinant protein expression fails, a scientist might blame faulty sequence data or a kit gone bad. But in the case of the ascomycete yeast Pachysolen tannophillus, researchers have identified a more fundamental problem: a CUG codon that normally translates to leucine instead results in alanine. This alternative coding, which joins another known nuclear sense codon reassignment in yeast, has been reported independently in two publications: a May Genome Research paper and another study, published this week (August 17) in PNAS. The authors of both papers have noted that their discoveries in P. tannophillus may be relevant to certain biotech applications involving the microbe as well as the study of RNA-based evolution in yeast.
The other known alternate sense codon use among yeast was first identified in Candida albicans two decades ago. This too involves a CUG codon, but results in serine in the translated protein.
“For this event to happen twice in a different linage is unexpected,” said Manuel Santos, the director of the Institute for Biomedicine at the University of Aveiro, Portugal, who was not involved with either study.
Santos, who has studied the CUG-serine reassignment extensively, told The Scientist that while a coding change may eventually confer an evolutionary fitness advantage, the initial reassignment comes at a substantial cost. Replacing bulky hydrophobic leucine with alanine or serine—both small, polar amino acids—could disrupt the structures and functions of critical proteins. Because the change is at the level ...
