Expression and processing of an unusual tRNA gene cluster in the cyanobacterium Anabaena sp. PCC 7120.

Anabaena sp. PCC 7120 is a filamentous cyanobacterium that bears a cluster of 26 t RNA genes and pseudogenes in the delta plasmid. The sequences of these t RNAs suggest that they have been acquired by horizontal gene transfer from another organism. The cluster is transcribed as a single transcript that is quickly processed to individual t RNAs. RNase P and RNase Z, in vitro, are able to process precursors containing some of these t RNAs. Deletion of the cluster causes no obvious phenotype or effect on growth under diverse culture conditions, indicating that the t RNAs encoded in the cluster are not required for growth under laboratory conditions, although they are aminoacylated in vivo. We have studied a possible t RNASer [t RNASer GCU(2)] present in the cluster with a sequence that deviates from consensus. This t RNA is processed in vitro by RNase P at the expected position. In addition, this t RNASer GCU is specifically aminoacylated with serine by an Anabaena sp. PCC 7120 crude extract. These data indicate that t RNASer GCU(2) is fully functional, despite its unusual structure. Similar clusters are found in other three cyanobacteria whose genomes have been sequenced. [ABSTRACT FROM AUTHOR]