Genes for ribosomal proteins S3, L16, L5 and S14 are clustered in the mitochondrial genome of Brassica napus L.

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We have cloned and sequenced an 8.9-kb mitochondrial-DNA fragment from rapeseed (Brassica napus L.). The nucleotide sequence indicates a gene cluster that encodes four ribosomal proteins (S3, L16, L5, S14), two tRNA genes (trnD, trnK), and the 5' region of the cob gene. The arrangement of these seven genes is trnD-trnK-rps3-rpl16-rpl5-rps14-cob. The rps3 and rpl16 frames overlap by 131 bp. The rpl5 and rps14 genes are separated by a 4-bp spacer. A 1474-basepair intron is located in the rps3 gene. The tRNA(Asp) gene (trnD) is very similar to the corresponding gene from chloroplasts (cp-like-tRNA(Asp)). Gene-specific probes for each ribosomal protein gene, and for the cp-like-trnD, trnK and cob genes, hybridized to a common pre-mRNA of an estimated size of 10 kilobases, indicating that these seven genes may be expressed as a single transcription unit. The rps3-rpl16-rpl5-rps14 region of B. napus mtDNA may function as a ribosomal operon, similar to the S10 and SPC operons of Escherichia coli and to the ribosomal protein operon of the chloroplast genome from Euglena gracilis.