Complex RNA maturation pathway for a chloroplast ribosomal protein operon with an internal tRNA cistron.
Open Access
- 1 July 1990
- journal article
- research article
- Published by Oxford University Press (OUP) in Plant Cell
- Vol. 2 (7) , 659-671
- https://doi.org/10.1105/tpc.2.7.659
Abstract
We have studied the expression of a large chloroplast ribosomal protein operon from Euglena gracilis that resembles the Escherichia coli S10 and spc ribosomal protein operons. We present evidence that 11 ribosomal protein genes, a tRNA gene, and a new locus, orf214/orf302, are expressed as a single transcription unit. The primary transcript also contains at least 15 group II and group III introns. Gene-specific probes for each ribosomal protein gene, orf214/orf302, and for trnl hybridized to a common pre-mRNA of an estimated size of 8.3 kilobases. This is the RNA size predicted for a full-length transcript of the entire operon after splicing of all 15 introns. Polycistronic ribosomal protein mRNAs accumulated primarily as spliced hepta-, hexa-, penta-, tetra-, tri-, and dicistronic mRNAs, which were presumed to arise by stepwise processing of the 8.3-kilobase pre-mRNA. A novel finding was the cotranscription of the trnl gene as an internal cistron within the ribosomal protein operon. Several combined mRNA/tRNA molecules, such as the pentacistronic rpl5-rps8-rpl36-trnl-rps14, were characterized. The occurrence of the orf214/orf302 is a unique feature of the Euglena operon, distinguishing it from all chloroplast and prokaryotic ribosomal protein operons characterized to date. The orf214/orf302 are not similar to any known genes but are cotranscribed with the ribosomal protein loci and encode stable RNA species of 2.4, 1.8, and 1.4 kilobases.This publication has 35 references indexed in Scilit:
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