HETEROCYST-FORMING FILAMENTOUS CYANOBACTERIA ENCODE PROTEINS THAT RESEMBLE EUKARYOTIC RNA-BINDING PROTEINS OF THE RNP FAMILY

Heterocyst-forming cyanobacteria have multiple genes encoding proteins that are similar to the RNP family of eukaryotic RNA-binding proteins. Three genes from two strains of cyanobacteria (Anabaena and Chlorogloeopsis) have been sequenced. All three putative gene products contain a single RNA Recognition Motif (RRM) that includes the highly conserved RNP1 and RNP2 regions and all three have an auxiliary motif consisting either of a short glycine-rich carboxy-terminal tail or a carboxy-terminal tail rich in both asparagine and glycine. RNA-binding protein genes are abundant in heterocyst-forming filamentous cyanobacteria but are not abundant in non-heterocyst-forming filamentous or unicellular cyanobacteria suggesting that the cyanobacterial proteins may play a role in gene expression during heterocyst differentiation. The cyanobacterial gene products share a significant degree of similarity with the RNP family of RNA-binding proteins which includes snRNP proteins, hnRNP proteins, nucleolins, as well as some regulatory proteins and some plant chloroplast proteins. Although the exact function of the cyanobacterial gene products is not yet known, their similarity to eukaryotic proteins suggests that they may play a role in RNA processing and metabolism. Finally, the presence of these genes in cyanobacteria has implications for the evolution of RNA binding proteins and RNA processing. © 1994 Academic Press Limited.