Cotranscription of 5S rRNA-tRNA(Arg)(ACG) from Brassica napus chloroplastsand processing of their intergenic spacer

S1 mapping showed that at least a significant portion of the 5S rRNA and tR N(Arg)(ACG) is co-transcribed in canola chloroplast, making trnR the last g ene transcribed in an operon of which the final sequence is 5'-16S-tRNA(Ile )-tRNA(Ala)-23S-4.5S-5S-tRNA(Arg)-3'. Various RNA termini representing RNA processing sites at several parts of the 5S rRNA-tRNA(Arg) area were detect ed. This gene spacer is substantially conserved among various species compa red here, and a secondary structure model for this chloroplast region in ca nola applies to other plant sequences. The conservation of this intergenic sequence suggests a functional role, possibly by providing recognition stru ctures for endogenous RNases involved in its maturing process. (C) 2000 Els evier Science B.V. All rights reserved.