Identification of 10Sa RNA (tmRNA) homologues from the cyanobacterium Synechococcus sp. strain PCC6301 and related organisms.

We have isolated the 10Sa RNA (tmRNA) from the unicellular cyanobacterium Synechococcus sp. strain PCC6301. It comprises of 394 nucleotides (nt) and has 55% homology to Escherichia coli tmRNA. The cloning and sequencing of the corresponding gene have revealed that, like in many tRNA genes, the terminal CCA sequence reported in all the tmRNA species characterized so far is not encoded in the DNA. Hybridization analysis has shown that the tmRNA gene is present as a single copy. Fairly high levels of tmRNA accumulate throughout the cell cycle; however, a slight increase in its level is observed during late-log to stationary phase. This suggests that tmRNA is functional not only when cells divide actively but also when cell growth stops.