KH domain proteins: Another family of bacterial RNA matchmakers?

In many bacteria, the stabilities and functions of small regulatory RNAs (sRNAs) that act by base pairing with target RNAs most often are dependent on Hfq or ProQ/FinO-domain proteins, two classes of RNA chaperone proteins. However, while all bacteria appear to have sRNAs, many have neither Hfq nor ProQ/FinO-domain proteins raising the question of whether another factor might act as an sRNA chaperone in these organisms. Several recent studies have reported that KH domain proteins, such as KhpA and KhpB, bind sRNAs. Here we describe what is known about the distribution, structures, RNA-binding properties, and physiologic roles of KhpA and KhpB and discuss evidence for and against these proteins serving as sRNAs chaperones.