Euglena gracilischloroplast ribosomal protein operon: a new chloroplast gene for ribosomal protein L5 and description of a novel organelle intron category designated group III

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Abstract
We describe the structure (3840 bp) of a novel Euglena gracilis chloroplast ribosomal protein operon that encodes the five genes rpll6-rpll4-rpl5-rps8-rpl36. The gene organization resembles the spc and the 3′-end of the S10 ribosomal protein operons of E. coli. The rpl5 is a new chloroplast gene not previously reported for any chloroplast genome to date and also not described as a nuclear-encoded, chloroplast protein gene. The operon contains at least 7 introns. We present evidence from primer extension analysis of chloroplast RNA for the correct in vivo splicing of five of the introns. Two of the introns within the rps8 gene flank an 8 bp exon, the smallest exon yet characterized in a chloroplast gene. Three introns resemble the classical group II introns of organelle genomes. The remaining 4 introns appear to be unique to the Euglena chloroplast DNA. They are uniform in size (95–109 nt), share common features with each other and are distinct from both group I and group II introns. We designate this new intron category as ‘group III’.