The FLAG peptide, a versatile fusion tag for the purification of recombinant proteins

Novel approaches to map protein interactions

Although we now have the sequence of the human genome at hand, we face the challenge of assigning function to the identified genes. Genes usually ascribe their function through proteins, and the role of proteins is to interact with other molecules. Therefore, if we could map the interactions of proteins we would be able to understand protein function. The challenge of mapping protein interactions is vast and many novel approaches have recently been developed for this task using molecular biology, mass spectrometry and chemiproteomic techniques.

Competition between SsrA tagging and translational termination at weak stop codons in Escherichia coli

SsrA is a tmRNA involved in tagging polypeptides on stalled ribosomes. The resulting fusion proteins are then degraded. We purified endogenous SsrA-tagged proteins by means of a genetically engineered SsrA and identified some of them. Analysis of the proteins suggested that they are tagged at their C-terminal extremities. One of them, ribokinase, is expressed from a messenger with a poorly efficient stop codon, leading to translational recoding events. A change in the ribokinase coding sequence from a weak to a strong translational stop sequence (UGAc to UAAu) annihilated SsrA tagging. Translational termination by UGA recruits the translational release factor (RF) 2. We observed that SsrA tagging of ribokinase was inversely correlated with RF2 activity, revealing a dynamic competition between translational termination and SsrA tagging.