. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. Poslflon along the Qenome Position along the Genome IEMO Position along the Genome Figure 1. "Purine-excess" curves for selected mitochondria! DNAs. In order from left to right—TOP: Saccharomyces cerevisiae (baker's yeast), Anemia franciscana (brine shrimp), Latimeria chalumnae (coela- canth); BOTTOM: Prototheca wickerhamii (chlorophyte alga), Drosophila melanogaster (fruitfly). Pan trog- lodytes (chimpanzee). The ordinate is the purine excess calculated for the presented (displayed) strand, as retrieved from GenBa
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. Poslflon along the Qenome Position along the Genome IEMO Position along the Genome Figure 1. "Purine-excess" curves for selected mitochondria! DNAs. In order from left to right—TOP: Saccharomyces cerevisiae (baker's yeast), Anemia franciscana (brine shrimp), Latimeria chalumnae (coela- canth); BOTTOM: Prototheca wickerhamii (chlorophyte alga), Drosophila melanogaster (fruitfly). Pan trog- lodytes (chimpanzee). The ordinate is the purine excess calculated for the presented (displayed) strand, as retrieved from GenBank. Position numbering follows the deposited sequence where in most cases position 1 was arbitrarily chosen within the D-loop region. Since the molecules are circular, the starting points for the curves have no special significance, though they tend to fall close to the H (heavy) strand origin of replication. nomes depicted in Figure 1 represent clear anomalies, how- ever. In these cases (and many others not shown), the majority of the ORFs display decreasing purine excess in the tran- scribed direction. Considering that these are highly "derived" mitochondria! genomes with only a few remaining genes from the ancestral set (6), their anomalous behavior can be readily explained. The proteins they encode are specialized compo- nents of the inner mitochondria! membrane and hence are composed mostly of hydrophobic amino acids whose codons are pyrimidine-rich. For the highly derived genomes (beyond Latimeria), all but one of the ORFs are situated on the dis- played strand (transcribed from left to right) and show the negative purine excess corresponding to hydrophobic proteins. The short initial segment of each of these genomes (cf. curve for chimpanzee mtDNA in Fig. 1) has a positive purine excess; this segment encodes ribosomal RNA—a gene product not translated, and thus unaffected by the relationship between the properties of the amino acid side-chains and the compo
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
