A recombinant polypeptide is described including at least one PUF RNA-binding domain capable of specifically binding to a cytosine RNA base. The PUF RNA-binding domain of the polypeptide includes at least one RNA base-binding motif of the general formula X.sub.1X.sub.2X.sub.3X.sub.4X.sub.5X.sub.6X.sub.7X.sub.8X.sub.9X.sub.10X.sub.11 wherein X.sub.1 is selected from a defined group and wherein the RNA base-binding motif is operably capable of specifically binding to a cytosine RNA base.

A novel class of transporter protein, referred to as SWEET, GLUE or Gl, is disclosed. These transporters provide a novel system for the transportation of sugars across membranes within a cell and between the inside and outside of a cell. Such transporters are useful for understanding and altering the sugar concentration within certain organs of an organism, and within certain organelles within the cell. These transporters are also useful in protecting plants from a pathogen attack.

The invention provides an isolated peptide comprising a lactylated lysine and a specific affinity reagent that specifically binds to a lactylated lysine in a peptide. Also provided are a method for detecting a lactylated lysine in a protein or a fragment thereof using the affinity reagent and a method for isolating the affinity reagent.