Figure 5. Example for a functional asRNA that is not conserved.

(A) Transcriptional organization and expression of the psbA2 locus in Synechocystis 6803 and 6714. The mRNAs of the very closely related genes psbA2 and 3 are positively regulated by light in both strains, whereas the asRNAs PsbA2R and PsbA3R²² originating from a TSS 19 nt upstream of the start codon (TU12 and TU1885) are specific for Synechocystis 6803. (B) The absence of PsbA2R in Synechocystis 6714 was verified by Northern blots. The 5S rRNA was used as a loading control (the psbA2 membrane is shown). (C) Alignment of the promoter sequences for PsbA2R and PsbA3R with the corresponding regions in Synechocystis 6714 indicate only two mismatches between the two strains. Of these, a single transition TATAAT → TATGAT within the −10 element (boxed) is likely involved in the activation/deactivation of the aTSS. For orientation, the psbA start codon on the reverse strand is shown in bold, and the direction of translation is indicated by the arrow bar.