Partial Sequence Analysis of the 5S to 18S rRNA Gene Region of the Maize Mitochondrial Genome

Abstract

The nucleotide sequence has been determined for a 664-base pair region of maize (Zea mays L.) mtDNA which contains the 3' end of the 18S rRNA gene, the 5S rRNA gene, and an intergenic region of 108 base pairs. Specific regions of the 18S rRNA gene show striking homology with the corresponding gene in Escherichia coli.The organization and structure of the rRNA genes in plant mitochondria are different from those of animals and fungi. In plant mitochondria, rRNA genes are larger and a 5S RNA is found in mitochondrial ribosomes (6, 15). The 5S and 18S rRNA genes in plant mtDNA are closely linked (3, 10, 12), but both are separate from the 26S rRNA gene (24). In maize, the 26S rRNA gene is separated from the 18S and 5S by 16,000 base pairs (bp) of DNA (24). Each of the rRNA genes is encoded by a single gene (24).This organization of 18S and 5S rRNA genes is unique to plant mtDNA. Prokaryotes have clusters of 16S, 23S, and 5S genes in that order. Chloroplasts usually have an organization like prokaryotes. Most eukaryotic nuclei have clusters of 5S genes which are unlinked to the 18S and 28S rRNA genes (17). To study the structure of plant mitochondrial rRNA genes, we have isolated a cloned fragment which contains the linked genes of 18S and 5S rRNA and determined a portion of the nucleotide sequence.The section of the molecule which has been sequenced contains part of the 18S rRNA gene and a complete 5S rRNA gene. We have located the 5S gene by sequence homology using the published sequence of the 5S rRNA from the mitochondria of wheat (22). Similarly, the location of the 3' end of the 18S gene was found because of strong homology with the corresponding genes of E. coli and maize chloroplast. The location of these boundary sequences defines the intergenic region which is 8 bp long and establishes the orientation and direction of transcription of both 18S and 5S rRNA genes.The large degree of homology found between the mitochondrial sequence and the bacterial sequence provides further support for the view that plant mitochondria have an endosymbiotic-eubacterial origin (2, 9, 10).

Identification of Two Methionine Transfer RNA Genes in the Maize Mitochondrial Genome

“…The presence of these tRNA genes complements the findings of Chao et al (9) who suggest by analysis of rRNA genes that the genome of maize mitochondria is more closely related to eubacteria than are the mitochondria of yeast or mammals.…”

“…The mitochondrial genome of maize is considerably more complex than the mammalian mitochondrial genome and its organization is not well understood. Three maize mitochondrial genes encoding 5S, 18S, and 26S rRNAs have been identified and characterized; these genes appear more closely related to eubacterial rRNA genes than are their mammalian counterparts (9,10,12 (6). The various plasmid DNAs were digested with the restriction enzyme EcoRI and the DNA fragments separated by gel electrophoresis on 1.5% agarose gels.…”

S2 episome of maize mitochondria encodes a 130-kilodalton protein found in male sterile and fertile plants

“…These results extend previous studies of the integrated S2 sequences in these and similar revertants in which no transcripts were detectable (15,19,31). The lack of expression of the integrated S2 episomes in these cytoplasmic revertants may be explained by the finding that a deletion removing at least 62% of the 5' untranslated region of URF1, including the terminus of the S2 episome, is characteristic of the integrated episome forms in these cytoplasmic revertants (19,31 (Fig. 1) …”

Nucleotide sequence and genome characterization of rice yellow mottle virus RNA

“…The serine (S) change in the catalytic site of RYMV and SBMV proteases in comparison to cellular and cysteine proteases of the other virus is shown in bold. (Chao et al,, 1983), the wheat mitochondrial 18S rRNA (Spencer et al, 1984) The 3" untranslated region of RYMV RNA contains 245 nt. Using the same computer program and algorithm, the last 147 nt of the RNA show a structure with a AG of 532.1,105 kJ with a pseudoknot domain (nt -92 to -147, relative to the 3" nucleotides) and a stem-loop domain (nt -1 to -91, relative to the 3' nucleotides) (Fig.…”