Printed in Great Britain 4 . 5 S Ribonucleic Acid , a Novel Ribosome Component in the Chloroplasts of Flowering Plants

A species of low-molecular-weight ribosomal RNA, referred to as '4.5 S rRNA', was found in addition to 5 S rRNA in the large subunit of chloroplast ribosomes of a wide range of flowering plants. It was shown by sequence analysis that several variants of this RNA may occur in a plant. Furthermore, although in most flowering plants the predominant variant contains about 100 nucleotides, in the broad bean it has less than 80. It seems, therefore, to be much more diverse in size and sequence than the other ribosomal RNA species. Like 5S rRNA, it does not contain modified nucleotides and it is also unusual in having an unphosphorylated 5'-end. It is apparently neither a homologue of cytosol 5.8S rRNA nor a fragment of 23 S rRNA.