Abstract
The 23S ribosomal RNA from higher plant chloroplasts is characterized by its dissociation into smaller fragments found in denaturing conditions. This fragmentation is a consequence of the cleavage at specific stem loops, and this specific break is called as "hidden break". The physiological function and introduction mechanism of the hidden break remain to be elucidated. We isolated the nara12 (the gene necessary for the achievement of RuBisCO accumulation) mutant and revealed that the DEAD-box RNA helicase 39 functions in a hidden break generation in Arabidopsis chloroplasts. Our analysis of the mutant plant suggests that the hidden break influences the translational efficiency of the ribosomes without any impairment of polysome formation. Furthermore, the introduction of the hidden break is highly induced in the plastids actively synthesizing proteins. These findings raise the possibility that the hidden break functions as a regulatory moiety to determine the ribosomal translation efficiency.
