The apocytochrome b gene in maize mitochondria does not contain introns and is preceded by a potential ribosome binding site

Abstract

The apocytochrome b (COB) gene has been isolated from maize (Zea mays L.) mitochondrial DNA. Sequence analysis reveals that the coding region of the gene is 1164 bp long and, in contrast with the homologous gene from yeast, does not contain introns or TGA (Trp) codons. The predicted polypeptide encoded by the gene has a mol. wt. of 42 868 daltons, and shows ˜48% amino acid sequence homology with the corresponding yeast and mammalian polypeptides. Hydropathic profiles of the polypeptide indicate the presence of nine, membrane spanning hydrophobic domains suggesting that it is organised in the inner mitochondrial membrane in a similar fashion to that proposed for apocytochrome b in other organisms. The COB gene is preceded by a sequence 5′ ‐AGTTGTCA‐3′ which may act as a ribosome binding site in the mRNA since: (i) it shows 67.5% complementarity with an octanucleotide at the 3′ end of the maize mitochondrial 18S rRNA, located in a position homologous to that of the Escherichia coli Shine and Dalgarno sequence, and (ii) a similar sequence precedes several other plant mitochondrial genes at a distance of 15–20 nucleotides from the ATG initiation codon. RNA transcript analysis shows that the gene is transcribed in a complex manner with the presumed mature mRNA (˜2.25 kb) probably being derived by sequential processing from a larger primary transcript.

Stoichiometric Shifts in the Common Bean Mitochondrial Genome Leading to Male Sterility and Spontaneous Reversion to Fertility

“…Amplification between atpA and cob utilized the following primers: primer P2 (5Ј-ATAGCAGGT-CTAATTCCGCG-3Ј) is homologous to the atpA gene from common bean at positions 1084 to 1103 (Chase and Ortega, 1992), and primer P8757 (5Ј-AGCTATGCATTACACACCTC-3Ј) was derived from the maize cob gene at positions 168 to 187 (Dawson et al, 1984). These Molecules are diagrammed to correspond to those presented in Figure 6.…”

Nucleotide Sequence of the F1-ATPase α Subunit Gene from Maize Mitochondria

“…First, it has been proposed that an octanucleotide segment from the 3' end of the mitochondrial 18S rRNA may act as a mRNA binding site in an analogous fashion to the prokaryotic Shine and Dalgarno sequence (3,25 Fig. 3).…”

“…It has been suggested that this fourth residue may be involved in additional base pairing with the formylmethionine tRNA anticodon loop allowing for greater specificity in translational initiation (3). Sequence data from the wheat (9) and maize (18) (5) genes from maize mitochondria contain either guanine (subunit 6 and a) or thymine (subunit 9) residues in the fourth position.…”

RNA editing in the cytochrome b locus of the higher plant Oenothera berteriana includes a U-to-C transition.

“…2). In several instances, the arginine codon CGG has been found in plant mitochondrial genes in which the amino acid tryptophan is conserved in the corresponding protein sequences of other species and has appropriately been discussed as potentially coding tryptophan instead of arginine (7,9,11,14). The RNA editing process now appears to change the cytidine residue in these codons to a uridine, thereby altering the codon and obliterating the need for a deviant genetic code in plant mitochondria.…”